1 Intro to Javascript
Recap
Programming Languages - set of instructions/code
which tells a computer what it needs to do
To make software or drivers
Scripting Languages -to perform some certain task.
used to create a website.
Markup Languages - prepare the structure/design
of a page
used to design a website
2
Client Side Scripting
3
CS380
Why use client-side programming?
4
client-side scripting (JavaScript) benefits:
usability:can modify a page without having to post
back to the server (faster UI)
efficiency: can make small, quick changes to page
without waiting for server
event-driven: can respond to user actions like clicks and
key presses
CS380
What is Javascript?
6
a lightweight programming language ("scripting
language")
used to make web pages interactive
insert dynamic text into HTML (ex: user name)
react to events (ex: page load user click)
get information about a user's computer (ex: browser
type)
perform calculations on user's computer (ex: form
validation)
CS380
A Simple Script
<html>
<head><title>First JavaScript Page</title></head>
<body>
<h1>First JavaScript Page</h1>
<script type="text/javascript">
document.write("<hr>");
document.write("Hello World Wide Web");
document.write("<hr>");
</script>
</body>
</html>
Linking to a JavaScript file:
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script
<script src="filename" type="text/javascript"></script>
HTML
script tag should be placed in HTML page's head
script code is stored in a separate .js file
JS code can be placed directly in the HTML file's
body or head (like CSS)
Data Types
Primitive data types
Number: integer & floating-point numbers
Boolean: true or false
String: a sequence of alphanumeric characters
Composite data types (or Complex data types or reference data
types )
Object: a named collection of data
Array: a sequence of values (an array is actually a predefined object)
Special data types
Null: the only value is "null" – to represent nothing.
Undefined: the only value is "undefined" – to represent the value of an
unintialized variable
Variables
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var name = expression; JS
var clientName = "Connie Client";
var age = 32;
var weight = 127.4; JS
variables are declared with the var keyword (case
sensitive)
types are not specified, but JS does have types
("loosely typed")
can find out a variable's type by calling typeof
typeof operator
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<head>
<script language=“JavaScript”>
var x = “hello”, y;
alert(“Variable x value is “ + typeof(x));
alert(“Variable y value is “ + typeof(y));
alert(“Variable x value is “ + typeof(z));
</script>
</head>
An unary operator that tells the type of its
operand.
Returnsa string which can be "number", "string",
"boolean", "object", "function", "undefined", and
"null"
Number type
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var enrollment = 99;
var medianGrade = 2.8;
var credits = 5 + 4 + (2 * 3);
JS
integers and real numbers are the same type (no int
vs. double)
same operators: + - * / % ++ -- = += -= *= /=
%=
similar precedence to Java
many operators auto-convert types: "2" * 3 is 6
CS380
Comments (same as Java)
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// single-line comment
/* multi-line comment */
JS
identical to Java's comment syntax
recall: 4 comment syntaxes
HTML: <!-- comment -->
CSS/JS/PHP: /* comment */
Java/JS/PHP: // comment
PHP: # comment
CS380
Special values: null and undefined
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var ned = null;
var benson = 9;
// at this point in the code,
// ned is null
// benson's 9
// caroline is undefined
JS
undefined : has not been declared, does not
exist
null : exists, but was specifically assigned an
empty or null value
CS380
Null & Undefined example
19 <html>
<head>
<title> Null and Undefined example </title>
<script language=“JavaScript”>
var test1, test2 = null;
alert(“No value assigned to the variable” + test1);
alert(“A null value was assigned” + test2);
</script>
</head>
<body> … </body>
</html>
Logical operators
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> < >= <= && || ! == != === !==
most logical operators automatically convert types:
5 < "7" is true
42 == 42.0 is true
"5.0" == 5 is true
=== and !== are strict equality tests; checks both
type and value
"5.0" === 5 is false
CS380
Type Conversion
Converting a value to a number
var numberVar = someVariable – 0;
Converting a value to a string
var stringVar = someVariable + "";
Converting a value to a boolean
var boolVar = !!someVariable;
== vs ===
// Type conversion is performed before comparison
var v1 = ("5" == 5); // true
// No implicit type conversion.
// True if only if both types and values are equal
var v2 = ("5" === 5); // false
var v3 = (5 === 5.0); // true
var v4 = (true == 1); // true (true is converted to 1)
var v5 = (true == 2); // false (true is converted to 1)
var v6 = (true == "1") // true
Boolean type
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var iLike190M = true;
var ieIsGood = "IE6" > 0; // false
if ("web devevelopment is great") { /* true */ }
if (0) { /* false */ }
JS
any value can be used as a Boolean
"false" values: 0, 0.0, NaN, "", null, and undefined
"truth" values: anything else
converting a value into a Boolean explicitly:
var boolValue = Boolean(otherValue);
var boolValue = !!(otherValue);
Boolean value example
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<head>
<script language=“JavaScript”>
var result;
result = (true*10 + false*7);
alert(“true*10 + false*7 = “, result);
</script>
</head>
The expression is converted to
(1*10 + 0*7) = 10
They are automatically converted.
if/else statement (same as Java)
25
if (condition) {
statements;
} else if (condition) {
statements;
} else {
statements;
}
JS
identical structure to Java's if/else statement
JavaScript allows almost anything as a condition
for loop (same as Java)
26
var sum = 0;
for (var i = 0; i < 100; i++) {
sum = sum + i;
} JS
var s1 = "hello";
var s2 = "";
for (var i = 0; i < s.length; i++) {
s2 += s1.charAt(i) + s1.charAt(i);
}
// s2 stores "hheelllloo" JS
while loops (same as Java)
27
while (condition) {
statements;
} JS
do {
statements;
} while (condition);
JS
break and continue keywords also behave as in
Java
Popup boxes
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alert("message"); // message
confirm("message"); // returns true or false
prompt("message"); // returns user input string
JS
alert(), confirm(), and prompt()
<script type="text/javascript">
alert("This is an Alert method");
confirm("Are you OK?");
prompt("What is your name?");
prompt("How old are you?","20");
</script>
Arrays
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var name = []; // empty array
var name = [value, value, ..., value]; // pre-filled
name[index] = value; // store element
JS
var ducks = ["Huey", "Dewey", "Louie"];
var stooges = []; // stooges.length is 0
stooges[0] = "Larry"; // stooges.length is 1
stooges[1] = "Moe"; // stooges.length is 2
stooges[4] = "Curly"; // stooges.length is 5
stooges[4] = "Shemp"; // stooges.length is 5
JS
Array methods
31
var a = ["Stef", "Jason"]; // Stef, Jason
a.push("Brian"); // Stef, Jason, Brian
a.unshift("Kelly"); // Kelly, Stef, Jason, Brian
a.pop(); // Kelly, Stef, Jason
a.shift(); // Stef, Jason
a.sort(); // Jason, Stef
JS
array serves as many data structures: list, queue,
stack, ...
methods: concat, join, pop, push, reverse, shift,
slice, sort, splice, toString, unshift
push and pop add / remove from back
unshift and shift add / remove from front
shift and pop return the element that is removed
String type
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var s = "Connie Client";
var fName = s.substring(0, s.indexOf(" ")); // "Connie"
var len = s.length; // 13
var s2 = 'Melvin Merchant';
JS
methods: charAt, charCodeAt, fromCharCode,
indexOf, lastIndexOf, replace, split,
substring, toLowerCase, toUpperCase
charAt returns a one-letter String (there is no char type)
length property (not a method as in Java)
Strings can be specified with "" or ''
concatenation with + :
1 + 1 is 2, but "1" + 1 is "11"
More about String
33
escape sequences behave as in Java: \' \" \& \n \t
\\
converting between numbers and Strings:
var count = 10;
var s1 = "" + count; // "10"
var s2 = count + " bananas, ah ah ah!"; // "10 bananas, ah
ah ah!"
var n1 = parseInt("42 is the answer"); // 42
var n2 = parseFloat("booyah"); // NaN JS
accessing the letters of a String:
var firstLetter = s[0]; // fails in IE
var firstLetter = s.charAt(0); // does work in IE
var lastLetter = s.charAt(s.length - 1); JS
Splitting strings: split and join
34
var s = "the quick brown fox";
var a = s.split(" "); // ["the", "quick", "brown", "fox"]
a.reverse(); // ["fox", "brown", "quick", "the"]
s = a.join("!"); // "fox!brown!quick!the"
JS
split breaks apart a string into an array using a
delimiter
can also be used with regular expressions (seen later)
join merges an array into a single string, placing a
delimiter between them
Math object
35
var rand1to10 = Math.floor(Math.random() * 10 + 1);
var three = Math.floor(Math.PI);
JS
methods: abs, ceil, cos, floor, log,
max, min, pow, random, round, sin,
sqrt, tan
properties: E, PI
Event-driven programming
36
split breaks apart a string into an array using a
delimiter
can also be used with regular expressions (seen later)
join merges an array into a single string, placing a
delimiter between them
Event-driven programming
37
you are used to programs start with a main method
(or implicit main like in PHP)
JavaScript programs instead wait for user actions
called events and respond to them
event-driven programming: writing programs driven
by user events
Let's write a page with a clickable button that pops
up a "Hello, World" window...
Buttons
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<button>Click me!</button> HTML
button's text appears inside tag; can also contain
images
To make a responsive button or other UI control:
1. choose the control (e.g. button) and event (e.g. mouse
1. click) of interest
2. write a JavaScript function to run when the event
occurs
3. attach the function to the event on the control
JavaScript functions
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function name() {
statement ;
statement ;
...
statement ;
} JS
function myFunction() {
alert("Hello!");
alert("How are you?");
} JS
the above could be the contents of example.js
linked to our HTML page
statements placed into functions can be evaluated in
response to user events
Event handlers
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<element attributes onclick="function();">...
HTML
<button onclick="myFunction();">Click me!</button>
HTML
JavaScript functions can be set as event handlers
when you interact with the element, the function will execute
onclick is just one of many event HTML attributes we'll
use
but popping up an alert window is disruptive and
annoying
A better user experience would be to have the message
appear on the page...
Document Object Model (DOM)
41
most JS code manipulates
elements on an HTML page
we can examine elements'
state
e.g. see whether a box is
checked
we can change state
e.g. insert some new text into
a div
we can change styles
e.g. make a paragraph red
DOM element objects
42
Accessing elements:
document.getElementById
43
document.getElementById returns the DOM object
for an element with a given id
can change the text inside most elements by setting
the innerHTML property
can change the text in form controls by setting the
value property
Accessing elements:
document.getElementById
44
var name = document.getElementById("id");
JS
<button onclick="changeText();">Click me!</button>
<span id="output">replace me</span>
<input id="textbox" type="text" /> HTML
function changeText() {
var span = document.getElementById("output");
var textBox = document.getElementById("textbox");
textbox.style.color = "red";
} JS
Changing element style:
element.style
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Attribute Property or style object
color color
padding padding
background-color backgroundColor
border-top-width borderTopWidth
Font size fontSize
Font famiy fontFamily
Preetify
46
function changeText() {
//grab or initialize text here
// font styles added by JS:
text.style.fontSize = "13pt";
text.style.fontFamily = "Comic Sans MS";
text.style.color = "red"; // or pink?
} JS
document.getElementById
Used to change anything in your document (web
page) that has an id
Then, change different aspects of the element with
that id:
<img src = “zombie.jpg” height = “500” width = “300”
alt = “eat your brain” id = “img1”>
Use document.getElementById to change the:
src
height
width
alt
getElementById()
<!DOCTYPE html>
<html>
<head>
<meta charset= "utf-8" />
</head>
<body style = "background-color:#000000; color: red;">
<h1> Hello</h1>
<p> <img src = "ball.jpg" width = "100" height = "100"
alt = "a ball picture" id = "ball1"></p>
<script>
var x = prompt("What size should the ball's width be?")
document.getElementById("ball1").width = x
</script>
</body>
</html>
getElementById to change CSS style:
<!DOCTYPE html><html><head> <meta charset= "utf-8" /></head>
<body>
<p id = "firstp"> This is a paragraph</p>
<p id = "secondp">This is a second paragraph</p>
<script>
document.getElementById("firstp").style.color = "#9999FF";
document.getElementById("firstp").style.fontSize = "120%";
document.getElementById("firstp").style.backgroundColor="#332277";
document.getElementById("firstp").style.textAlign = "right";
document.getElementById("firstp").style.padding = "30px";
document.getElementById("firstp").style.borderWidth = "8px";
document.getElementById("firstp").style.borderColor = "green";
document.getElementById("firstp").style.borderStyle = "inset";
</script>
</body></html>
innerHTML
The innerHTML is what is between the opening and the closing tag,
regardless of what the tag is:
<p id = “firstp”> This is the innerHTML text because it goes between the
opening and closing tag
</p>
Above, the innerHTML is: “This is the innerHTML text because it goes between
the opening and closing tag”
To change it:
document.getElementById(“firstp”).innerHTML = “new text for paragraph”
<h1 id = “firsth”>Title goes here </h1>
Above: innerHTML is: Title goes here
To change:
document.getElementById(“firsth”).innerHTML = “New Title”
innerHTML (cont.)
<p id = “linked”> <a href = “udel.edu” id = “firstlink”> link to udel </a>
</p>
What is the innerHTML of linked?
What is the innerHTML of firstlink?
How would you change the innerHTML of linked to a new link?
<ol id = “list1”>
<li id = “firstItem”> cats </li>
<li id=“seconditem”> dogs </li>
</ol>
What is the innerHTML of list1?
What is the innerHTML of firstitem?
How would you change the innerHTML of list1 to a new list?
What about this one?
<script>
var PicArr = new Array()
PicArr[0] = "cute1.jpg"
PicArr[1] = "cute2.jpg"
PicArr[2] = "cute3.jpg"
PicArr[3] = "cute4.jpg"
PicArr[4] = "cute5.jpg"
var NameArr = new Array()
NameArr[0] = "lion cubs"
NameArr[1] = "hedgehogs"
NameArr[2] = "otter pup"
NameArr[3] = "kitten"
NameArr[4] = "panda babies“
var num = Math.floor(Math.random() * 5)
document.write("<p><img src = \" "+PicArr[num]+"\"></p>")
/*aside – where do the quotes start and stop here and why? */
document.write("<p>" + NameArr[num] + "</p>")
</script>
How about this?
<script>
var myArray = new Array()
myArray[0] = "hey"
myArray[1] = "hi"
myArray[2] = "wassup"
myArray[3] = "greetings"
myArray[4] = "howdie“
var num = Math.floor(Math.random() * 5)
document.write("<p> " + myArray[num] + "</p>")
</script>
What does this do?
<script> var ans = prompt(“pick a number between 0 and 4”)
var EngArr = new Array() var frenchans = prompt("What is the French translation of " +
EngArr[0] = "dog" EngArr[ans] + "?")
EngArr[1] = "cat"
EngArr[2] = "hello" if (frenchans.toLowerCase() == FrenchArr[ans])
EngArr[3] = "Thank you" { document.write("<p> You're right! </p>")
EngArr[4] = "bunny" }
var FrenchArr = new Array() else
FrenchArr[0] = "chien" {
FrenchArr[1] = "chat" document.write("<p> Sorry. You're no good at this. </p>")
FrenchArr[2] = "bonjour" }
FrenchArr[3] = "merci" </script>
FrenchArr[4] = "lapin“
