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PHP Module 2

web programming using PHP - Calicut University 5th sem BSc Computer science

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78 views64 pages

PHP Module 2

web programming using PHP - Calicut University 5th sem BSc Computer science

Uploaded by

uzhunnanshinana
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 64

1 Yuvakshetra Institute of Management Studies- PHP Notes (BSc.

CS 2017-20 Batch)

UNIT- II
JAVASCRIPT

JavaScript is a lightweight, interpreted programming language. It is designed for creating


network-centric applications. It is complimentary to and integrated with Java. JavaScript is
very easy to implement because it is integrated with HTML. It is open and cross-platform.
JavaScript is a dynamic computer programming language. It is lightweight and most commonly
used as a part of web pages, whose implementations allow client-side script to interact with the
user and make dynamic pages. It is an interpreted programming language with object-oriented
capabilities.

CLIENT SIDE PROGRAMMING

Client-side JavaScript is the most common form of the language. The script should be included
in or referenced by an HTML document for the code to be interpreted by the browser.
It means that a web page need not be a static HTML, but can include programs that interact
with the user, control the browser, and dynamically create HTML content.
The JavaScript client-side mechanism provides many advantages over traditional CGI server-
side scripts. For example, you might use JavaScript to check if the user has entered a valid e-
mail address in a form field.
The JavaScript code is executed when the user submits the form, and only if all the entries are
valid, they would be submitted to the Web Server.
JavaScript can be used to trap user-initiated events such as button clicks, link navigation, and
other actions that the user initiates explicitly or implicitly.

ADVANTAGES OF JAVASCRIPT

The merits of using JavaScript are −


 Less server interaction − You can validate user input before sending the page off to
the server. This saves server traffic, which means less load on your server.
 Immediate feedback to the visitors − They don't have to wait for a page reload to see
if they have forgotten to enter something.
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 Increased interactivity − You can create interfaces that react when the user hovers
over them with a mouse or activates them via the keyboard.
 Richer interfaces − You can use JavaScript to include such items as drag-and-drop
components and sliders to give a Rich Interface to your site visitors.

LIMITATIONS OF JAVASCRIPT
We cannot treat JavaScript as a full-fledged programming language. It lacks the following
important features −
 Client-side JavaScript does not allow the reading or writing of files. This has been kept
for security reason.
 JavaScript cannot be used for networking applications because there is no such support
available.
 JavaScript doesn't have any multi-threading or multiprocessor capabilities.

JAVASCRIPT – SYNTAX

SCRIPT TAG

JavaScript can be implemented using JavaScript statements that are placed within the
<script>... </script> HTML tags in a web page.
You can place the <script> tags, containing your JavaScript, anywhere within your web page,
but it is normally recommended that you should keep it within the <head> tags.
The <script> tag alerts the browser program to start interpreting all the text between these tags
as a script. A simple syntax of your JavaScript will appear as follows.

<script ...>
JavaScript code
</script>
The script tag takes two important attributes −

Language − This attribute specifies what scripting language you are using. Typically, its value
will be javascript. Although recent versions of HTML (and XHTML, its successor) have
phased out the use of this attribute.
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Type − This attribute is what is now recommended to indicate the scripting language in use and
its value should be set to "text/javascript".

So your JavaScript segment will look like −

<script language = "javascript" type = "text/javascript">


JavaScript code
</script>

JAVASCRIPT EXAMPLE

Let us take a sample example to print out "Hello World". We added an optional HTML
comment that surrounds our JavaScript code. This is to save our code from a browser that
does not support JavaScript. The comment ends with a "//-->". Here "//" signifies a comment
in JavaScript, so we add that to prevent a browser from reading the end of the HTML comment
as a piece of JavaScript code. Next, we call a function document.write which writes a string
into our HTML document.
This function can be used to write text, HTML, or both. Take a look at the following code.

<html>
<body>
<script language = "javascript" type = "text/javascript">
<!--
document.write("Hello World!")
//-->
</script>
</body>
</html>

This code will produce the following result −

Hello World!
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WHITESPACE AND LINE BREAKS


JavaScript ignores spaces, tabs, and newlines that appear in JavaScript programs. You can use
spaces, tabs, and newlines freely in your program and you are free to format and indent your
programs in a neat and consistent way that makes the code easy to read and understand.
Semicolons are Optional
Simple statements in JavaScript are generally followed by a semicolon character, just as they
are in C, C++, and Java. JavaScript, however, allows you to omit this semicolon if each of
your statements are placed on a separate line. For example, the following code could be written
without semicolons.

<script language = "javascript" type = "text/javascript">

<!--

var1 = 10

var2 = 20

//-->

</script>

But when formatted in a single line as follows, you must use semicolons −

<script language = "javascript" type = "text/javascript">


<!--
var1 = 10; var2 = 20;
//-->
</script>

Note − It is a good programming practice to use semicolons.

Case Sensitivity
JavaScript is a case-sensitive language. This means that the language keywords, variables,
function names, and any other identifiers must always be typed with a consistent capitalization
of letters.So the identifiers Time and TIME will convey different meanings in JavaScript.
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COMMENTS IN JAVASCRIPT

JavaScript supports both C-style and C++-style comments, Thus −


 Any text between a // and the end of a line is treated as a comment and is ignored by
JavaScript.
 Any text between the characters /* and */ is treated as a comment. This may span
multiple lines.
 JavaScript also recognizes the HTML comment opening sequence <!--. JavaScript
treats this as a single-line comment, just as it does the // comment.
 The HTML comment closing sequence --> is not recognized by JavaScript so it should
be written as //-->.
Example
The following example shows how to use comments in JavaScript.

<script language = "javascript" type = "text/javascript">


<!--
// This is a comment. It is similar to comments in C++

/*
* This is a multi-line comment in JavaScript
* It is very similar to comments in C Programming
*/
//-->
</script>

<NOSCRIPT> TAGS

If you have to do something important using JavaScript, then you can display a warning
message to the user using <noscript> tags.

You can add a noscript block immediately after the script block as follows −

<html>
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<body>
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<script language = "javascript" type = "text/javascript">


<!--
document.write("Hello World!")
//-->
</script>

<noscript>
Sorry...JavaScript is needed to go ahead.
</noscript>
</body>
</html>

Now, if the user's browser does not support JavaScript or JavaScript is not enabled, then the
message from </noscript> will be displayed on the screen.

JAVASCRIPT – INCLUDING JAVASCRIPT IN HTML

There is a flexibility given to include JavaScript code anywhere in an HTML document.


However the most preferred ways to include JavaScript in an HTML file are as follows −

 Script in <head>...</head> section.


 Script in <body>...</body> section.
 Script in <body>...</body> and <head>...</head> sections.
 Script in an external file and then include in <head>...</head> section.

JavaScript in <head>...</head> section


If you want to have a script run on some event, such as when a user clicks somewhere, then
you will place that script in the head as follows –

<html>
<head>
<script type = "text/javascript">

<!--
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function sayHello() {
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alert("Hello World")
}
//-->
</script>
</head>

<body>
<input type = "button" onclick = "sayHello()" value = "Say Hello" />
</body>
</html>

JavaScript in <body>...</body> section


If you need a script to run as the page loads so that the script generates content in the page,
then the script goes in the <body> portion of the document. In this case, you would not have
any function defined using JavaScript. Take a look at the following code.

<html>
<head>
</head>

<body>
<script type = "text/javascript">
<!--
document.write("Hello World")
//-->
</script>

<p>This is web page body </p>


</body>
</html>

JavaScript in <body> and <head> Sections


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You can put your JavaScript code in <head> and <body> section altogether as follows −
8 Yuvakshetra Institute of Management Studies- PHP Notes (BSc.CS 2017-20 Batch)

<html>
<head>
<script type = "text/javascript">
<!--
function sayHello() {
alert("Hello World")
}
//-->
</script>
</head>

<body>
<script type = "text/javascript">
<!--
document.write("Hello World")
//-->
</script>

<input type = "button" onclick = "sayHello()" value = "Say Hello" />


</body>
</html>

JavaScript in External File

As you begin to work more extensively with JavaScript, you will be likely to find that there
are cases where you are reusing identical JavaScript code on multiple pages of a site.

You are not restricted to be maintaining identical code in multiple HTML files. The script tag
provides a mechanism to allow you to store JavaScript in an external file and then include it
into your HTML files.

Here is an example to show how you can include an external JavaScript file in your HTML
code using script tag and its src attribute.
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<html>
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<head>
<script type = "text/javascript" src = "filename.js" ></script>
</head>

<body>
.......
</body>
</html>

To use JavaScript from an external file source, you need to write all your JavaScript source
code in a simple text file with the extension ".js" and then include that file as shown above.

For example, you can keep the following content in filename.js file and then you can
use sayHello function in your HTML file after including the filename.js file.

function sayHello() {
alert("Hello World")
}

JAVASCRIPT DATATYPES

One of the most fundamental characteristics of a programming language is the set of data
types it supports. These are the type of values that can be represented and manipulated in a
programming language.

JavaScript allows you to work with three primitive data types −

 Numbers, eg. 123, 120.50 etc.

 Strings of text e.g. "This text string" etc.

 Boolean e.g. true or false.

JavaScript also defines two trivial data types, null and undefined, each of which defines only
a single value. In addition to these primitive data types, JavaScript supports a composite data
type known as object.
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JAVASCRIPT VARIABLES
Like many other programming languages, JavaScript has variables. Variables can be thought
of as named containers. You can place data into these containers and then refer to the data
simply by naming the container.

Before you use a variable in a JavaScript program, you must declare it. Variables are declared
with the var keyword as follows.

<script type = "text/javascript">


<!--
var money;
var name;
//-->
</script>
You can also declare multiple variables with the same var keyword as follows −

<script type = "text/javascript">


<!--
var money, name;
//-->
</script>
Storing a value in a variable is called variable initialization. You can do variable
initialization at the time of variable creation or at a later point in time when you need that
variable.

For instance, you might create a variable named money and assign the value 2000.50 to it
later. For another variable, you can assign a value at the time of initialization as follows.

<script type = "text/javascript">

<!--

var name = "Ali";

var money;

money = 2000.50;

//-->

</script>

Note − Use the var keyword only for declaration or initialization, once for the life of any
variable name in a document. You should not re-declare same variable twice.
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JavaScript is untyped language. This means that a JavaScript variable can hold a value of any
data type. Unlike many other languages, you don't have to tell JavaScript during variable
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declaration what type of value the variable will hold. The value type of a variable can change
during the execution of a program and JavaScript takes care of it automatically.

JavaScript Variable Scope


The scope of a variable is the region of your program in which it is defined. JavaScript
variables have only two scopes.

 Global Variables − A global variable has global scope which means it can be defined
anywhere in your JavaScript code.

 Local Variables − A local variable will be visible only within a function where it is
defined. Function parameters are always local to that function.

Within the body of a function, a local variable takes precedence over a global variable with
the same name. If you declare a local variable or function parameter with the same name as a
global variable, you effectively hide the global variable. Take a look into the following
example.

<html>
<body onload = checkscope();>
<script type = "text/javascript">
<!--
var myVar = "global"; // Declare a global variable
function checkscope( ) {
var myVar = "local"; // Declare a local variable
document.write(myVar);
}
//-->
</script>
</body>
</html>

This produces the following result −

local
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JavaScript Variable Names


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While naming your variables in JavaScript, keep the following rules in mind.

 You should not use any of the JavaScript reserved keywords as a variable name. These
keywords are mentioned in the next section. For example, break or boolean variable
names are not valid.

 JavaScript variable names should not start with a numeral (0-9). They must begin with
a letter or an underscore character. For example, 123test is an invalid variable name
but _123test is a valid one.

 JavaScript variable names are case-sensitive. For example, Name and name are two
different variables.

JAVASCRIPT – OPERATORS

What is an Operator?
Let us take a simple expression 4 + 5 is equal to 9. Here 4 and 5 are called operands and ‘+’
is called the operator. JavaScript supports the following types of operators.

 Arithmetic Operators
 Comparison Operators
 Logical (or Relational) Operators
 Assignment Operators
 Conditional (or ternary) Operators
Arithmetic Operators
JavaScript supports the following arithmetic operators −

Assume variable A holds 10 and variable B holds 20, then −

Sr.No. Operator & Description

1 + (Addition)
Adds two operands
Ex: A + B will give 30

2 - (Subtraction)
Subtracts the second operand from the first
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Ex: A - B will give -10


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3 * (Multiplication)
Multiply both operands
Ex: A * B will give 200

4 / (Division)
Divide the numerator by the denominator
Ex: B / A will give 2

5 % (Modulus)
Outputs the remainder of an integer division
Ex: B % A will give 0

6 ++ (Increment)
Increases an integer value by one
Ex: A++ will give 11

7 -- (Decrement)
Decreases an integer value by one
Ex: A-- will give 9

Note − Addition operator (+) works for Numeric as well as Strings. e.g. "a" + 10 will give
"a10".

Example
The following code shows how to use arithmetic operators in JavaScript.

<html>
<body>

<script type = "text/javascript">


<!--
var a = 33;
var b = 10;
var c = "Test";
var linebreak = "<br />";

document.write("a + b = ");
result = a + b;
document.write(result);
document.write(linebreak);
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document.write("a - b = ");
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result = a - b;
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document.write(result);
document.write(linebreak);

document.write("a / b = ");
result = a / b;
document.write(result);
document.write(linebreak);

document.write("a % b = ");
result = a % b;
document.write(result);
document.write(linebreak);

document.write("a + b + c = ");
result = a + b + c;
document.write(result);
document.write(linebreak);

a = ++a;
document.write("++a = ");
result = ++a;
document.write(result);
document.write(linebreak);

b = --b;
document.write("--b = ");
result = --b;
document.write(result);
document.write(linebreak);
//-->
</script>

Set the variables to different values and then try...


</body>
</html>

Output
a + b = 43
a - b = 23
a / b = 3.3
a%b=3
a + b + c = 43Test
++a = 35
--b = 8
Set the variables to different values and then try...
14

Comparison Operators
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JavaScript supports the following comparison operators −


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Assume variable A holds 10 and variable B holds 20, then −

Sr.No. Operator & Description

1 = = (Equal)
Checks if the value of two operands are equal or not, if yes, then the condition
becomes true.
Ex: (A == B) is not true.

2 != (Not Equal)
Checks if the value of two operands are equal or not, if the values are not equal,
then the condition becomes true.
Ex: (A != B) is true.

3 > (Greater than)


Checks if the value of the left operand is greater than the value of the right operand,
if yes, then the condition becomes true.
Ex: (A > B) is not true.

4 < (Less than)


Checks if the value of the left operand is less than the value of the right operand,
if yes, then the condition becomes true.
Ex: (A < B) is true.

5 >= (Greater than or Equal to)


Checks if the value of the left operand is greater than or equal to the value of the
right operand, if yes, then the condition becomes true.
Ex: (A >= B) is not true.

6 <= (Less than or Equal to)


Checks if the value of the left operand is less than or equal to the value of the right
operand, if yes, then the condition becomes true.
Ex: (A <= B) is true.

Example
15

The following code shows how to use comparison operators in JavaScript.


Page

<html>
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<body>
<script type = "text/javascript">
<!--
var a = 10;
var b = 20;
var linebreak = "<br />";

document.write("(a == b) => ");


result = (a == b);
document.write(result);
document.write(linebreak);

document.write("(a < b) => ");


result = (a < b);
document.write(result);
document.write(linebreak);

document.write("(a > b) => ");


result = (a > b);
document.write(result);
document.write(linebreak);

document.write("(a != b) => ");


result = (a != b);
document.write(result);
document.write(linebreak);
document.write("(a >= b) => ");
result = (a >= b);
document.write(result);
document.write(linebreak);
document.write("(a <= b) => ");
result = (a <= b);
document.write(result);
document.write(linebreak);
//-->
</script>
Set the variables to different values and different operators and then try...
</body>
</html>

Output
16

(a == b) => false
(a < b) => true
Page

(a > b) => false


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(a != b) => true
(a >= b) => false
a <= b) => true
Set the variables to different values and different operators and then try...

Logical Operators
JavaScript supports the following logical operators −

Assume variable A holds 10 and variable B holds 20, then −

Sr.No. Operator & Description

1 && (Logical AND)


If both the operands are non-zero, then the condition becomes true.
Ex: (A && B) is true.

2 || (Logical OR)
If any of the two operands are non-zero, then the condition becomes true.
Ex: (A || B) is true.

3 ! (Logical NOT)
Reverses the logical state of its operand. If a condition is true, then the Logical
NOT operator will make it false.
Ex: ! (A && B) is false.

Example
Try the following code to learn how to implement Logical Operators in JavaScript.

<html>
<body>
<script type = "text/javascript">
<!--
var a = true;
var b = false;
var linebreak = "<br />";

document.write("(a && b) => ");


result = (a && b);
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document.write(result);
Page

document.write(linebreak);
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document.write("(a || b) => ");


result = (a || b);
document.write(result);
document.write(linebreak);

document.write("!(a && b) => ");


result = (!(a && b));
document.write(result);
document.write(linebreak);
//-->
</script>
<p>Set the variables to different values and different operators and then try...</p>
</body>
</html>

Output
(a && b) => false
(a || b) => true
!(a && b) => true
Set the variables to different values and different operators and then try...

Bitwise Operators
JavaScript supports the following bitwise operators −

Assume variable A holds 2 and variable B holds 3, then −

Sr.No. Operator & Description

1 & (Bitwise AND)


It performs a Boolean AND operation on each bit of its integer arguments.
Ex: (A & B) is 2.

2 | (BitWise OR)
It performs a Boolean OR operation on each bit of its integer arguments.
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Ex: (A | B) is 3.
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3 ^ (Bitwise XOR)
It performs a Boolean exclusive OR operation on each bit of its integer arguments.
Exclusive OR means that either operand one is true or operand two is true, but not
both.
Ex: (A ^ B) is 1.

4 ~ (Bitwise Not)
It is a unary operator and operates by reversing all the bits in the operand.
Ex: (~B) is -4.

5 << (Left Shift)


It moves all the bits in its first operand to the left by the number of places specified
in the second operand. New bits are filled with zeros. Shifting a value left by one
position is equivalent to multiplying it by 2, shifting two positions is equivalent to
multiplying by 4, and so on.
Ex: (A << 1) is 4.

6 >> (Right Shift)


Binary Right Shift Operator. The left operand’s value is moved right by the
number of bits specified by the right operand.
Ex: (A >> 1) is 1.

7 >>> (Right shift with Zero)


This operator is just like the >> operator, except that the bits shifted in on the left
are always zero.
Ex: (A >>> 1) is 1.

Example
Try the following code to implement Bitwise operator in JavaScript.

<html>
<body>
<script type = "text/javascript">
<!--
var a = 2; // Bit presentation 10
var b = 3; // Bit presentation 11
var linebreak = "<br />";
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document.write("(a & b) => ");


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result = (a & b);


document.write(result);
document.write(linebreak);

document.write("(a | b) => ");


result = (a | b);
document.write(result);
document.write(linebreak);

document.write("(a ^ b) => ");


result = (a ^ b);
document.write(result);
document.write(linebreak);

document.write("(~b) => ");


result = (~b);
document.write(result);
document.write(linebreak);

document.write("(a << b) => ");


result = (a << b);
document.write(result);
document.write(linebreak);

document.write("(a >> b) => ");


result = (a >> b);
document.write(result);
document.write(linebreak);
//-->
</script>
<p>Set the variables to different values and different operators and then try...</p>
</body>
</html>

(a & b) => 2
(a | b) => 3
(a ^ b) => 1
(~b) => -4
(a << b) => 16
(a >> b) => 0
Set the variables to different values and different operators and then try...
20

Assignment Operators
JavaScript supports the following assignment operators −
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Sr.No. Operator & Description

1 = (Simple Assignment )
Assigns values from the right side operand to the left side operand
Ex: C = A + B will assign the value of A + B into C

2 += (Add and Assignment)


It adds the right operand to the left operand and assigns the result to the left
operand.
Ex: C += A is equivalent to C = C + A

3 −= (Subtract and Assignment)


It subtracts the right operand from the left operand and assigns the result to the left
operand.
Ex: C -= A is equivalent to C = C - A

4 *= (Multiply and Assignment)


It multiplies the right operand with the left operand and assigns the result to the
left operand.
Ex: C *= A is equivalent to C = C * A

5 /= (Divide and Assignment)


It divides the left operand with the right operand and assigns the result to the left
operand.
Ex: C /= A is equivalent to C = C / A

6 %= (Modules and Assignment)


It takes modulus using two operands and assigns the result to the left operand.
Ex: C %= A is equivalent to C = C % A

Note − Same logic applies to Bitwise operators so they will become like <<=, >>=, >>=, &=,
|= and ^=.

Example
Try the following code to implement assignment operator in JavaScript.

<html>
<body>
<script type = "text/javascript">
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<!--
var a = 33;
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var b = 10;
var linebreak = "<br />";

document.write("Value of a => (a = b) => ");


result = (a = b);
document.write(result);
document.write(linebreak);

document.write("Value of a => (a += b) => ");


result = (a += b);
document.write(result);
document.write(linebreak);

document.write("Value of a => (a -= b) => ");


result = (a -= b);
document.write(result);
document.write(linebreak);

document.write("Value of a => (a *= b) => ");


result = (a *= b);
document.write(result);
document.write(linebreak);

document.write("Value of a => (a /= b) => ");


result = (a /= b);
document.write(result);
document.write(linebreak);

document.write("Value of a => (a %= b) => ");


result = (a %= b);
document.write(result);
document.write(linebreak);
22

//-->
Page

</script>
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<p>Set the variables to different values and different operators and then try...</p>
</body>
</html>

Output
Value of a => (a = b) => 10
Value of a => (a += b) => 20
Value of a => (a -= b) => 10
Value of a => (a *= b) => 100
Value of a => (a /= b) => 10
Value of a => (a %= b) => 0
Set the variables to different values and different operators and then try...

Miscellaneous Operator
We will discuss two operators here that are quite useful in JavaScript: the conditional
operator (? :) and the typeof operator.

Conditional Operator (? :)
The conditional operator first evaluates an expression for a true or false value and then
executes one of the two given statements depending upon the result of the evaluation.

Sr.No. Operator and Description

1 ? : (Conditional )

If Condition is true? Then value X : Otherwise value Y

Example
Try the following code to understand how the Conditional Operator works in JavaScript.

<html>
<body>
<script type = "text/javascript">
<!--
var a = 10;
var b = 20;
var linebreak = "<br />";

document.write ("((a > b) ? 100 : 200) => ");


result = (a > b) ? 100 : 200;
document.write(result);
23

document.write(linebreak);
Page

document.write ("((a < b) ? 100 : 200) => ");


24 Yuvakshetra Institute of Management Studies- PHP Notes (BSc.CS 2017-20 Batch)

result = (a < b) ? 100 : 200;


document.write(result);
document.write(linebreak);
//-->
</script>
<p>Set the variables to different values and different operators and then try...</p>
</body>
</html>

Output
((a > b) ? 100 : 200) => 200
((a < b) ? 100 : 200) => 100
Set the variables to different values and different operators and then try...

typeof Operator
The typeof operator is a unary operator that is placed before its single operand, which can be
of any type. Its value is a string indicating the data type of the operand.

The typeof operator evaluates to "number", "string", or "boolean" if its operand is a number,
string, or boolean value and returns true or false based on the evaluation.

Here is a list of the return values for the typeof Operator.

Type String Returned by typeof

Number "number"

String "string"

Boolean "boolean"

Object "object"

Function "function"

Undefined "undefined"

Null "object"

Example
The following code shows how to implement typeof operator.
24

<html>
Page

<body>
25 Yuvakshetra Institute of Management Studies- PHP Notes (BSc.CS 2017-20 Batch)

<script type = "text/javascript">


<!--
var a = 10;
var b = "String";
var linebreak = "<br />";

result = (typeof b == "string" ? "B is String" : "B is Numeric");


document.write("Result => ");
document.write(result);
document.write(linebreak);

result = (typeof a == "string" ? "A is String" : "A is Numeric");


document.write("Result => ");
document.write(result);
document.write(linebreak);
//-->
</script>
<p>Set the variables to different values and different operators and then try...</p>
</body>
</html>

Output
Result => B is String
Result => A is Numeric
Set the variables to different values and different operators and then try...

JAVASCRIPT - IF...ELSE STATEMENT

While writing a program, there may be a situation when you need to adopt one out of a given
set of paths. In such cases, you need to use conditional statements that allow your program to
make correct decisions and perform right actions.

JavaScript supports conditional statements which are used to perform different actions based
on different conditions. Here we will explain the if..else statement.

Flow Chart of if-else


The following flow chart shows how the if-else statement works.
25
Page
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JavaScript supports the following forms of if..else statement −

 if statement

 if...else statement

 if...else if... statement.

if statement
The if statement is the fundamental control statement that allows JavaScript to make decisions
and execute statements conditionally.

Syntax
The syntax for a basic if statement is as follows −

if (expression) {
Statement(s) to be executed if expression is true
}
Here a JavaScript expression is evaluated. If the resulting value is true, the given statement(s)
are executed. If the expression is false, then no statement would be not executed. Most of the
times, you will use comparison operators while making decisions.

Example
Try the following example to understand how the if statement works.

<html>
<body>
<script type = "text/javascript">
<!--
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var age = 20;


Page
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if( age > 18 ) {


document.write("<b>Qualifies for driving</b>");
}
//-->
</script>
<p>Set the variable to different value and then try...</p>
</body>
</html>

Output
Qualifies for driving
Set the variable to different value and then try...

if...else statement
The 'if...else' statement is the next form of control statement that allows JavaScript to execute
statements in a more controlled way.

Syntax
if (expression) {
Statement(s) to be executed if expression is true
} else {
Statement(s) to be executed if expression is false
}
Here JavaScript expression is evaluated. If the resulting value is true, the given statement(s)
in the ‘if’ block, are executed. If the expression is false, then the given statement(s) in the else
block are executed.

Example
Try the following code to learn how to implement an if-else statement in JavaScript.

<html>
<body>
<script type = "text/javascript">
<!--
var age = 15;

if( age > 18 ) {


document.write("<b>Qualifies for driving</b>");
} else {
document.write("<b>Does not qualify for driving</b>");
}
//-->
</script>
27

<p>Set the variable to different value and then try...</p>


</body>
Page

</html>
28 Yuvakshetra Institute of Management Studies- PHP Notes (BSc.CS 2017-20 Batch)

Output
Does not qualify for driving
Set the variable to different value and then try...

if...else if... statement


The if...else if... statement is an advanced form of if…else that allows JavaScript to make a
correct decision out of several conditions.

Syntax
The syntax of an if-else-if statement is as follows −

if (expression 1) {
Statement(s) to be executed if expression 1 is true
} else if (expression 2) {
Statement(s) to be executed if expression 2 is true
} else if (expression 3) {
Statement(s) to be executed if expression 3 is true
} else {
Statement(s) to be executed if no expression is true
}
There is nothing special about this code. It is just a series of if statements, where each if is a
part of the else clause of the previous statement. Statement(s) are executed based on the true
condition, if none of the conditions is true, then the else block is executed.

Example
Try the following code to learn how to implement an if-else-if statement in JavaScript.

<html>
<body>
<script type = "text/javascript">
<!--
var book = "maths";
if( book == "history" ) {
document.write("<b>History Book</b>");
} else if( book == "maths" ) {
document.write("<b>Maths Book</b>");
} else if( book == "economics" ) {
document.write("<b>Economics Book</b>");
} else {
document.write("<b>Unknown Book</b>");
}
//-->
</script>
<p>Set the variable to different value and then try...</p>
28

</body>
Page

<html>
29 Yuvakshetra Institute of Management Studies- PHP Notes (BSc.CS 2017-20 Batch)

Output
Maths Book
Set the variable to different value and then try...

JAVASCRIPT - SWITCH CASE

You can use multiple if...else…if statements, as in the previous chapter, to perform a
multiway branch. However, this is not always the best solution, especially when all of the
branches depend on the value of a single variable.

Starting with JavaScript 1.2, you can use a switch statement which handles exactly this
situation, and it does so more efficiently than repeated if...else ifstatements.

Flow Chart
The following flow chart explains a switch-case statement works.

Syntax
The objective of a switch statement is to give an expression to evaluate and several different
statements to execute based on the value of the expression. The interpreter checks
each case against the value of the expression until a match is found. If nothing matches,
a default condition will be used.
29

switch (expression) {
case condition 1: statement(s)
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break;

case condition 2: statement(s)


break;
...

case condition n: statement(s)


break;

default: statement(s)
}
The break statements indicate the end of a particular case. If they were omitted, the interpreter
would continue executing each statement in each of the following cases.

We will explain break statement in Loop Control chapter.

Example
Try the following example to implement switch-case statement.

<html>
<body>
<script type = "text/javascript">
<!--
var grade = 'A';
document.write("Entering switch block<br />");
switch (grade) {
case 'A': document.write("Good job<br />");
break;

case 'B': document.write("Pretty good<br />");


break;

case 'C': document.write("Passed<br />");


break;

case 'D': document.write("Not so good<br />");


break;

case 'F': document.write("Failed<br />");


break;

default: document.write("Unknown grade<br />")


}
document.write("Exiting switch block");
//-->
</script>
<p>Set the variable to different value and then try...</p>
30

</body>
Page

</html>
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Output
Entering switch block
Good job
Exiting switch block
Set the variable to different value and then try...
Break statements play a major role in switch-case statements. Try the following code that uses
switch-case statement without any break statement.

<html>

<body>

<script type = "text/javascript">

<!--

var grade = 'A';

document.write("Entering switch block<br />");

switch (grade) {

case 'A': document.write("Good job<br />");

case 'B': document.write("Pretty good<br />");

case 'C': document.write("Passed<br />");

case 'D': document.write("Not so good<br />");

case 'F': document.write("Failed<br />");

default: document.write("Unknown grade<br />")

document.write("Exiting switch block");

//-->

</script>

<p>Set the variable to different value and then try...</p>

</body>

</html>

Output
31

Entering switch block


Page

Good job
32 Yuvakshetra Institute of Management Studies- PHP Notes (BSc.CS 2017-20 Batch)

Pretty good
Passed
Not so good
Failed
Unknown grade
Exiting switch block
Set the variable to different value and then try..

JAVASCRIPT - WHILE LOOPS

While writing a program, you may encounter a situation where you need to perform an action
over and over again. In such situations, you would need to write loop statements to reduce the
number of lines.

JavaScript supports all the necessary loops to ease down the pressure of programming.

The while Loop


The most basic loop in JavaScript is the while loop which would be discussed in this chapter.
The purpose of a while loop is to execute a statement or code block repeatedly as long as
an expression is true. Once the expression becomes false, the loop terminates.

Flow Chart
The flow chart of while loop looks as follows −

Syntax
32

The syntax of while loop in JavaScript is as follows −


Page

while (expression) {
33 Yuvakshetra Institute of Management Studies- PHP Notes (BSc.CS 2017-20 Batch)

Statement(s) to be executed if expression is true


}

Example
Try the following example to implement while loop.

<html>
<body>

<script type = "text/javascript">


<!--
var count = 0;
document.write("Starting Loop ");

while (count < 10) {


document.write("Current Count : " + count + "<br />");
count++;
}

document.write("Loop stopped!");
//-->
</script>

<p>Set the variable to different value and then try...</p>


</body>
</html>

Output
Starting Loop
Current Count : 0
Current Count : 1
Current Count : 2
Current Count : 3
Current Count : 4
Current Count : 5
Current Count : 6
Current Count : 7
Current Count : 8
Current Count : 9
Loop stopped!
Set the variable to different value and then try...

The do...while Loop

The do...while loop is similar to the while loop except that the condition check happens at the
33

end of the loop. This means that the loop will always be executed at least once, even if the
Page

condition is false.
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Flow Chart
The flow chart of a do-while loop would be as follows −

Syntax
The syntax for do-while loop in JavaScript is as follows −

do {
Statement(s) to be executed;
} while (expression);
Note − Don’t miss the semicolon used at the end of the do...while loop.

Example
Try the following example to learn how to implement a do-while loop in JavaScript.

<html>
<body>
<script type = "text/javascript">
<!--
var count = 0;

document.write("Starting Loop" + "<br />");


do {
document.write("Current Count : " + count + "<br />");
count++;
}
34

while (count < 5);


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35 Yuvakshetra Institute of Management Studies- PHP Notes (BSc.CS 2017-20 Batch)

document.write ("Loop stopped!");


//-->
</script>
<p>Set the variable to different value and then try...</p>
</body>
</html>

Output
Starting Loop
Current Count : 0
Current Count : 1
Current Count : 2
Current Count : 3
Current Count : 4
Loop Stopped!
Set the variable to different value and then try...

JAVASCRIPT - FOR LOOP

The 'for' loop is the most compact form of looping. It includes the following three important
parts −

 The loop initialization where we initialize our counter to a starting value. The
initialization statement is executed before the loop begins.

 The test statement which will test if a given condition is true or not. If the condition
is true, then the code given inside the loop will be executed, otherwise the control will
come out of the loop.

 The iteration statement where you can increase or decrease your counter.

You can put all the three parts in a single line separated by semicolons.

Flow Chart
The flow chart of a for loop in JavaScript would be as follows −
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Syntax
The syntax of for loop is JavaScript is as follows −

for (initialization; test condition; iteration statement) {


Statement(s) to be executed if test condition is true
}

Example
Try the following example to learn how a for loop works in JavaScript.

<html>
<body>
<script type = "text/javascript">
<!--
var count;
document.write("Starting Loop" + "<br />");
for(count = 0; count < 10; count++) {
document.write("Current Count : " + count );
document.write("<br />");
}
document.write("Loop stopped!");
//-->
</script>
<p>Set the variable to different value and then try...</p>
</body>
</html>

Output
Starting Loop
Current Count : 0
Current Count : 1
Current Count : 2
Current Count : 3
Current Count : 4
Current Count : 5
Current Count : 6
Current Count : 7
Current Count : 8
Current Count : 9
36

Loop stopped!
Page

Set the variable to different value and then try...


37 Yuvakshetra Institute of Management Studies- PHP Notes (BSc.CS 2017-20 Batch)

JAVASCRIPT FOR...IN LOOP

The for...in loop is used to loop through an object's properties. As we have not discussed
Objects yet, you may not feel comfortable with this loop. But once you understand how objects
behave in JavaScript, you will find this loop very useful.

Syntax
The syntax of ‘for..in’ loop is −

for (variablename in object) {


statement or block to execute
}
In each iteration, one property from object is assigned to variablename and this loop
continues till all the properties of the object are exhausted.

Example
Try the following example to implement ‘for-in’ loop. It prints the web
browser’s Navigator object.

<html>
<body>
<script type = "text/javascript">
<!--
var aProperty;
document.write("Navigator Object Properties<br /> ");
for (aProperty in navigator) {
document.write(aProperty);
document.write("<br />");
}
document.write ("Exiting from the loop!");
//-->
</script>
<p>Set the variable to different object and then try...</p>
</body>
</html>

Output
Navigator Object Properties
37

serviceWorker
Page

webkitPersistentStorage
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webkitTemporaryStorage
geolocation
doNotTrack
onLine
languages
language
userAgent
product
platform
appVersion
appName
appCodeName
hardwareConcurrency
maxTouchPoints
vendorSub
vendor
productSub
cookieEnabled
mimeTypes
plugins
javaEnabled
getStorageUpdates
getGamepads
webkitGetUserMedia
vibrate
getBattery
sendBeacon
registerProtocolHandler
unregisterProtocolHandler
Exiting from the loop!
Set the variable to different object and then try...

JAVASCRIPT - LOOP CONTROL

JavaScript provides full control to handle loops and switch statements. There may be a
situation when you need to come out of a loop without reaching its bottom. There may also
be a situation when you want to skip a part of your code block and start the next iteration of
the loop.

To handle all such situations, JavaScript provides break and continue statements. These
statements are used to immediately come out of any loop or to start the next iteration of any
loop respectively.

THE BREAK STATEMENT


38

The break statement, which was briefly introduced with the switch statement, is used to exit
Page

a loop early, breaking out of the enclosing curly braces.


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Flow Chart
The flow chart of a break statement would look as follows −

Example
The following example illustrates the use of a break statement with a while loop. Notice how
the loop breaks out early once x reaches 5 and reaches to document.write (..) statement just
below to the closing curly brace −

<html>
<body>
<script type = "text/javascript">
<!--
var x = 1;
document.write("Entering the loop<br /> ");

while (x < 20) {


if (x == 5) {
break; // breaks out of loop completely
}
x = x + 1;
document.write( x + "<br />");
}
document.write("Exiting the loop!<br /> ");
//-->
</script>
39

<p>Set the variable to different value and then try...</p>


Page
40 Yuvakshetra Institute of Management Studies- PHP Notes (BSc.CS 2017-20 Batch)

</body>
</html>

Output
Entering the loop
2
3
4
5
Exiting the loop!
Set the variable to different value and then try...
We already have seen the usage of break statement inside a switch statement.

THE CONTINUE STATEMENT


The continue statement tells the interpreter to immediately start the next iteration of the loop
and skip the remaining code block. When a continue statement is encountered, the program
flow moves to the loop check expression immediately and if the condition remains true, then
it starts the next iteration, otherwise the control comes out of the loop.

Example
This example illustrates the use of a continue statement with a while loop. Notice how
the continue statement is used to skip printing when the index held in variable x reaches 5 −

<html>
<body>
<script type = "text/javascript">
<!--
var x = 1;
document.write("Entering the loop<br /> ");

while (x < 10) {


x = x + 1;

if (x == 5) {
continue; // skip rest of the loop body
}
document.write( x + "<br />");
40

}
Page

document.write("Exiting the loop!<br /> ");


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//-->
</script>
<p>Set the variable to different value and then try...</p>
</body>
</html>

Output
Entering the loop
2
3
4
6
7
8
9
10
Exiting the loop!
Set the variable to different value and then try...

USING LABELS TO CONTROL THE FLOW

Starting from JavaScript 1.2, a label can be used with break and continue to control the flow
more precisely. A label is simply an identifier followed by a colon (:) that is applied to a
statement or a block of code. We will see two different examples to understand how to use
labels with break and continue.

Note − Line breaks are not allowed between the ‘continue’ or ‘break’ statement and its label
name. Also, there should not be any other statement in between a label name and associated
loop.

Example 1
The following example shows how to implement Label with a break statement.

<html>
<body>
<script type = "text/javascript">
<!--
document.write("Entering the loop!<br /> ");
outerloop: // This is the label name
41

for (var i = 0; i < 5; i++) {


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document.write("Outerloop: " + i + "<br />");


innerloop:
for (var j = 0; j < 5; j++) {
if (j > 3 ) break ; // Quit the innermost loop
if (i == 2) break innerloop; // Do the same thing
if (i == 4) break outerloop; // Quit the outer loop
document.write("Innerloop: " + j + " <br />");
} }
document.write("Exiting the loop!<br /> ");
//-->
</script>
</body> </html>

Output
Entering the loop!
Outerloop: 0
Innerloop: 0
Innerloop: 1
Innerloop: 2
Innerloop: 3
Outerloop: 1
Innerloop: 0
Innerloop: 1
Innerloop: 2
Innerloop: 3
Outerloop: 2
Outerloop: 3
Innerloop: 0
Innerloop: 1
Innerloop: 2
Innerloop: 3
Outerloop: 4
42

Exiting the loop!


Page
43 Yuvakshetra Institute of Management Studies- PHP Notes (BSc.CS 2017-20 Batch)

JAVASCRIPT – FUNCTIONS

A function is a group of reusable code which can be called anywhere in your program. This
eliminates the need of writing the same code again and again. It helps programmers in writing
modular codes. Functions allow a programmer to divide a big program into a number of small
and manageable functions. Like any other advanced programming language, JavaScript also
supports all the features necessary to write modular code using functions. You must have seen
functions like alert() and write() in the earlier chapters. We were using these functions again
and again, but they had been written in core JavaScript only once.

Function Definition
Before we use a function, we need to define it. The most common way to define a function in
JavaScript is by using the function keyword, followed by a unique function name, a list of
parameters (that might be empty), and a statement block surrounded by curly braces.

Syntax
The basic syntax is shown here.

<script type = "text/javascript">


<!--
function functionname(parameter-list) {
statements
}
//-->
</script>

Example
Try the following example. It defines a function called say Hello that takes no parameters −

<script type = "text/javascript">


<!--
function sayHello() {
alert("Hello there");
}
//-->
</script>

Calling a Function
43

To invoke a function somewhere later in the script, you would simply need to write the name
Page

of that function as shown in the following code.


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<html>
<head>
<script type = "text/javascript">
function sayHello() {
document.write ("Hello there!");
}
</script>

</head>

<body>
<p>Click the following button to call the function</p>
<form>
<input type = "button" onclick = "sayHello()" value = "Say Hello">
</form>
<p>Use different text in write method and then try...</p>
</body>
</html>

Function Parameters
Till now, we have seen functions without parameters. But there is a facility to pass different
parameters while calling a function. These passed parameters can be captured inside the
function and any manipulation can be done over those parameters. A function can take
multiple parameters separated by comma.

Example
Try the following example. We have modified our say Hello function here. Now it takes two
parameters.

<html>
<head>
<script type = "text/javascript">
function sayHello(name, age) {
document.write (name + " is " + age + " years old.");
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}
Page
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</script>
</head>

<body>
<p>Click the following button to call the function</p>
<form>
<input type = "button" onclick = "sayHello('Zara', 7)" value = "Say Hello">
</form>
<p>Use different parameters inside the function and then try...</p>
</body>
</html>

The return Statement


A JavaScript function can have an optional return statement. This is required if you want to
return a value from a function. This statement should be the last statement in a function.

For example, you can pass two numbers in a function and then you can expect the function to
return their multiplication in your calling program.

Example
Try the following example. It defines a function that takes two parameters and concatenates
them before returning the resultant in the calling program.

<html>
<head>
<script type = "text/javascript">
function concatenate(first, last) {
var full;
full = first + last;
return full;
}
function secondFunction() {
var result;
45

result = concatenate('Zara', 'Ali');


Page
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document.write (result );
}
</script>
</head>

<body>
<p>Click the following button to call the function</p>
<form>
<input type = "button" onclick = "secondFunction()" value = "Call Function">
</form>
<p>Use different parameters inside the function and then try...</p>
</body>
</html>

JAVASCRIPT BUILT-IN FUNCTIONS

Number Methods
The Number object contains only the default methods that are part of every object's definition.

Sr.No. Method & Description

1. toFixed()
Formats a number with a specific number of digits to the right of the decimal.

2. toLocaleString()
Returns a string value version of the current number in a format that may vary
according to a browser's locale settings.

3. toPrecision()
Defines how many total digits (including digits to the left and right of the decimal)
to display of a number.

4. toString()
Returns the string representation of the number's value.

5. valueOf()
46

Returns the number's value.


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Boolean Methods
Here is a list of each method and its description.

Sr.No. Method & Description

1 toSource()

Returns a string containing the source of the Boolean object; you can use this string
to create an equivalent object.

2 toString()

Returns a string of either "true" or "false" depending upon the value of the object.

3 valueOf()

Returns the primitive value of the Boolean object.

String Methods
Here is a list of each method and its description.

Sr.No. Method & Description

1. charAt()
Returns the character at the specified index.

2. concat()
Combines the text of two strings and returns a new string.

3. length()
Returns the length of the string.

4. match()
Used to match a regular expression against a string.

5. replace()
Used to find a match between a regular expression and a string, and to replace the
matched substring with a new substring.

6. search()
47

Executes the search for a match between a regular expression and a specified
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string.
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7. split()
Splits a String object into an array of strings by separating the string into
substrings.

8. toLocaleLowerCase()
The characters within a string are converted to lower case while respecting the
current locale.

9. toLocaleUpperCase()
The characters within a string are converted to upper case while respecting the
current locale.

10. toLowerCase()
Returns the calling string value converted to lower case.

11. toString()
Returns a string representing the specified object.

12. toUpperCase()
Returns the calling string value converted to uppercase.

13. valueOf()
Returns the primitive value of the specified object.

Array Methods
Here is a list of each method and its description.

Sr.No. Method & Description

1. concat()
Returns a new array comprised of this array joined with other array(s) and/or
value(s).

2. indexOf()
Returns the first (least) index of an element within the array equal to the specified
value, or -1 if none is found.

3. join()
Joins all elements of an array into a string.
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4. pop()
Removes the last element from an array and returns that element.

5. push()
Adds one or more elements to the end of an array and returns the new length of
the array.

6. reverse()
Reverses the order of the elements of an array -- the first becomes the last, and the
last becomes the first.

7. sort()
Sorts the elements of an array.

8. toString()
Returns a string representing the array and its elements.

Date Methods
Here is a list of each method and its description.

Sr.No. Method & Description

1. Date()
Returns today's date and time

2. getDate()
Returns the day of the month for the specified date according to local time.

3. getDay()
Returns the day of the week for the specified date according to local time.

4. getFullYear()
Returns the year of the specified date according to local time.

5. getHours()
Returns the hour in the specified date according to local time.

6. getMilliseconds()
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Returns the milliseconds in the specified date according to local time.


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7. getMinutes()
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Returns the minutes in the specified date according to local time.

8. getMonth()
Returns the month in the specified date according to local time.

9. getSeconds()
Returns the seconds in the specified date according to local time.

10. getTime()
Returns the numeric value of the specified date as the number of milliseconds since
January 1, 1970, 00:00:00 UTC.

11. getYear()
Deprecated - Returns the year in the specified date according to local time. Use
getFullYear instead.

12. setDate()
Sets the day of the month for a specified date according to local time.

13. setFullYear()
Sets the full year for a specified date according to local time.

14. setHours()
Sets the hours for a specified date according to local time.

15. setMilliseconds()
Sets the milliseconds for a specified date according to local time.

16. setMinutes()
Sets the minutes for a specified date according to local time.

17. setMonth()
Sets the month for a specified date according to local time.

18. setSeconds()
Sets the seconds for a specified date according to local time.

19. setTime()
Sets the Date object to the time represented by a number of milliseconds since
January 1, 1970, 00:00:00 UTC.

20. setYear()
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Deprecated - Sets the year for a specified date according to local time. Use
setFullYear instead.
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Math Methods
Here is a list of each method and its description.

Sr.No. Method & Description

21. abs()
Returns the absolute value of a number.

22. acos()
Returns the arccosine (in radians) of a number.

23. asin()
Returns the arcsine (in radians) of a number.

24. atan()
Returns the arctangent (in radians) of a number.

25. cos()
Returns the cosine of a number.

26. exp()
Returns EN, where N is the argument, and E is Euler's constant, the base of the
natural logarithm.

27. max()
Returns the largest of zero or more numbers.

28. min()
Returns the smallest of zero or more numbers.

29. pow()
Returns base to the exponent power, that is, base exponent.

30. sin()
Returns the sine of a number.

31. sqrt()
Returns the square root of a number.

32. tan()
Returns the tangent of a number.

33. toSource()
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Returns the string "Math".


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JAVASCRIPT - DIALOG BOXES (POP-UP)

JavaScript supports three important types of dialog boxes. These dialog boxes can be used to
raise and alert, or to get confirmation on any input or to have a kind of input from the users.
Here we will discuss each dialog box one by one.

Alert Dialog Box


An alert dialog box is mostly used to give a warning message to the users. For example, if one
input field requires to enter some text but the user does not provide any input, then as a part
of validation, you can use an alert box to give a warning message.

Nonetheless, an alert box can still be used for friendlier messages. Alert box gives only one
button "OK" to select and proceed.

Example
<html>
<head>
<script type = "text/javascript">
<!--
function Warn() {
alert ("This is a warning message!");
document.write ("This is a warning message!");
}
//-->
</script>
</head>

<body>
<p>Click the following button to see the result: </p>
<form>
<input type = "button" value = "Click Me" onclick = "Warn();" />
</form>
</body>
</html>
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Confirmation Dialog Box

A confirmation dialog box is mostly used to take user's consent on any option. It displays a
dialog box with two buttons: OK and Cancel.

If the user clicks on the OK button, the window method confirm() will return true. If the user
clicks on the Cancel button, then confirm() returns false. You can use a confirmation dialog
box as follows.

Example
<html>
<head>
<script type = "text/javascript">
<!--
function getConfirmation() {
var retVal = confirm("Do you want to continue ?");
if( retVal == true ) {
document.write ("User wants to continue!");
return true;
} else {
document.write ("User does not want to continue!");
return false;
}
}
//-->
</script>
</head>

<body>
<p>Click the following button to see the result: </p>
<form>
<input type = "button" value = "Click Me" onclick = "getConfirmation();" />
</form>
</body>
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</html>
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Prompt Dialog Box

The prompt dialog box is very useful when you want to pop-up a text box to get user input.
Thus, it enables you to interact with the user. The user needs to fill in the field and then click
OK.

This dialog box is displayed using a method called prompt() which takes two parameters: (i)
a label which you want to display in the text box and (ii) a default string to display in the text
box.

This dialog box has two buttons: OK and Cancel. If the user clicks the OK button, the window
method prompt() will return the entered value from the text box. If the user clicks the Cancel
button, the window method prompt()returns null.

Example
The following example shows how to use a prompt dialog box −

<html>
<head>
<script type = "text/javascript">
<!--
function getValue() {
var retVal = prompt("Enter your name : ", "your name here");
document.write("You have entered : " + retVal);
}
//-->
</script>
</head>

<body>
<p>Click the following button to see the result: </p>
<form>
<input type = "button" value = "Click Me" onclick = "getValue();" />
</form>
</body>
</html>
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isNaN() Method
The Number.isNaN() method determines whether a value is NaN (Not-A-Number).

This method returns true if the value is of the type Number, and equates to NaN. Otherwise it
returns false.
Examples:
Input : 0/0
Output : true

Input : 213
Output : false

Input : '213'
Output : false

Input : 'hello'
Output : false

Input : NaN
Output : true

parseInt()

The parseInt() is an inbuilt function in JavaScript which is used to accept the string and
convert it into an integer. It actually returns an integer of the specified radix(base) which is
accepted as second parameter of the parseInt() function. If the string does not contain a
numeric value then it returns NaN i.e, not a number.

Syntax:

parseInt(Value, radix)
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Parameters:
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Value: “Value” contains a string which is converted to an integer.


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radix: This parameter represents the radix or base to be used and it is optional.

Return value: It returns a number and if the first character can’t be converted to a number
then the function returns NaN. It actually returns a number parsed up to that point where it
encounters a character which is not a number in the specified radix(base).

Example:

Input: var n = parseInt("2018@geeksforgeeks");

Output: n = 2018

Number() Function

Number() is an in built javascript function which is used to convert data type to number.

Syntax:

Number(query javascript variable)

Parameters: The parameter of the number function is the javascript variable which is user
input to be converted.The number function converts any type of javascript variable to
number type.

Return Values:
Number() function returns the number format for any type of javascript variable.
Examples:
Input : Number(true);
Number(false);
Output :
1
0
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JAVASCRIPT – EVENTS

What is an Event ?
JavaScript's interaction with HTML is handled through events that occur when the user or the
browser manipulates a page.

When the page loads, it is called an event. When the user clicks a button, that click too is an
event. Other examples include events like pressing any key, closing a window, resizing a
window, etc.

ONCLICK EVENT TYPE


This is the most frequently used event type which occurs when a user clicks the left button of
his mouse. You can put your validation, warning etc., against this event type.

Example
<html>
<head>
<script type = "text/javascript">
<!--
function sayHello() {
alert("Hello World")
}
//-->
</script>
</head>

<body>
<p>Click the following button and see result</p>
<form>
<input type = "button" onclick = "sayHello()" value = "Say Hello" />
</form>
</body>
</html>
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ONSUBMIT EVENT TYPE


onsubmit is an event that occurs when you try to submit a form. You can put your form
validation against this event type.

Example
The following example shows how to use onsubmit. Here we are calling a validate() function
before submitting a form data to the webserver. If validate() function returns true, the form
will be submitted, otherwise it will not submit the data.

Try the following example.

<html>
<head>
<script type = "text/javascript">
<!--
function validation() {
all validation goes here
.........
return either true or false
}
//-->
</script>
</head>

<body>
<form method = "POST" action = "t.cgi" onsubmit = "return validate()">
.......
<input type = "submit" value = "Submit" />
</form>
</body>
</html>
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HTML 5 STANDARD EVENTS


The standard HTML 5 events are listed here for your reference. Here script indicates a
Javascript function to be executed against that event.

Attribute Value Description

Offline script Triggers when the document goes offline

onblur script Triggers when the window loses focus

Triggers when media can start play, but might has to stop
oncanplay script
for buffering

Triggers when media can be played to the end, without


oncanplaythrough script
stopping for buffering

onchange script Triggers when an element changes

onclick script Triggers on a mouse click

ondrag script Triggers when an element is dragged

ondrop script Triggers when dragged element is being dropped

ondurationchange script Triggers when the length of the media is changed

Triggers when a media resource element suddenly becomes


onemptied script
empty.

onended script Triggers when media has reach the end

onerror script Triggers when an error occur


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onfocus script Triggers when the window gets focus


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onkeydown script Triggers when a key is pressed

onkeypress script Triggers when a key is pressed and released

onkeyup script Triggers when a key is released

onload script Triggers when the document loads

onmousedown script Triggers when a mouse button is pressed

onmousemove script Triggers when the mouse pointer moves

onmouseout script Triggers when the mouse pointer moves out of an element

onmouseover script Triggers when the mouse pointer moves over an element

onmouseup script Triggers when a mouse button is released

onprogress script Triggers when the browser is fetching the media data

onratechange script Triggers when the media data's playing rate has changed

onreadystatechange script Triggers when the ready-state changes

onredo script Triggers when the document performs a redo

onresize script Triggers when the window is resized

onscroll script Triggers when an element's scrollbar is being scrolled

onsubmit script Triggers when a form is submitted


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JAVASCRIPT - DOCUMENT OBJECT MODEL OR DOM

The way a document content is accessed and modified is called the Document Object Model,
or DOM. The Objects are organized in a hierarchy. This hierarchical structure applies to the
organization of objects in a Web document.

 Window object − Top of the hierarchy. It is the outmost element of the object
hierarchy.

 Document object − Each HTML document that gets loaded into a window becomes a
document object. The document contains the contents of the page.

 Form object − Everything enclosed in the <form>...</form> tags sets the form object.

 Form control elements − The form object contains all the elements defined for that
object such as text fields, buttons, radio buttons, and checkboxes.

The HTML DOM model is constructed as a tree of Objects:

The HTML DOM Tree of Objects

Example:

<Table>
<ROWS>
<TR>
<TD>Car</TD>
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<TD>Scooter</TD>
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</TR>
<TR>
<TD>MotorBike</TD>
<TD>Bus</TD>
</TR>
</ROWS>
</Table>

HTML DOM getElementById() Method


Example

Get the element with the specified ID:

document.getElementById("demo");
Definition and Usage

The getElementById() method returns the element that has the ID attribute with the specified
value.

This method is one of the most common methods in the HTML DOM, and is used almost
every time you want to manipulate, or get info from, an element on your document.

Returns null if no elements with the specified ID exists.

An ID should be unique within a page. However, if more than one element with the specified
ID exists, the getElementById() method returns the first element in the source code.

HTML DOM getElementsByName() Method


Example
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Get all elements with the specified name:


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var x = document.getElementsByName("fname");
Definition and Usage

The getElementsByName() method returns a collection of all elements in the document with
the specified name (the value of the name attribute), as a NodeList object.

The NodeList object represents a collection of nodes. The nodes can be accessed by index
numbers. The index starts at 0.

JAVASCRIPT OBJECTS

Objects, in JavaScript, is it’s most important data-type and forms the building blocks for
modern JavaScript. These objects are quite different from JavaScript’s primitive data-
types(Number, String, Boolean, null, undefined and symbol) in the sense that while these
primitive data-types all store a single value each (depending on their types).

 Objects are more complex and each object may contain any combination of these
primitive data-types as well as reference data-types.
 An object, is a reference data type. Variables that are assigned a reference value are
given a reference or a pointer to that value. That reference or pointer points to the
location in memory where the object is stored. The variables don’t actually store the
value.
 Loosely speaking, objects in JavaScript may be defined as an unordered collection
of related data, of primitive or reference types, in the form of “key: value”
pairs.These keys can be variables or functions and are called properties and methods,
respectively, in the context of an object.

Example

var person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};

Object Properties

The named values, in JavaScript objects, are called properties.

Property Value
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firstName John

lastName Doe

age 50

eyeColor blue

Using the JavaScript Keyword new

The following example also creates a new JavaScript object with four properties:

Example

var person = new Object();


person.firstName = "John";
person.lastName = "Doe";
person.age = 50;
person.eyeColor = "blue";

*************************************************************************
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