A minimal type checking library that I developed over a few years of programming JavaScript. It has a solid and minimalistic API surface that provides useful functions for basic type checking.

• All functions return true or false (no one throws)
• It is resistent to monkey patching or malicious prototype overriding
• It comes with TypeScript support out of the box.
• Thoroughly tested for edge cases
• Works in Node and Browsers (CommonJS out of the box)

Returns true if x is a non-null object.

Returns true if x is a function (including class methods, arrow functions, result of new Function(), etc.).

Returns true if x is a finite number.

• If min is a number, it'll also check that x.length >= min
• If max is a number, it'll also check that x.length <= max (note that it is an inclusive range)

Returns true if x is an integer number.

• If min is a number, it'll also check that x.length >= min
• If max is a number, it'll also check that x.length <= max (note that it is an inclusive range)

Returns true if x is a boolean

Returns true if x is a string.

• If minLength is a number, it'll also check that x.length >= minLength
• If maxLength is a number, it'll also check that x.length <= maxLength (note that it is an inclusive range)

Returns true if x is an array (Array.isArray()).

• If minLength is a number, it'll also check that x.length >= minLength
• If maxLength is a number, it'll also check that x.length <= maxLength (note that it is an inclusive range)

Returns true if x is an array or string and idx represents a valid index to it (0 <= idx && idx < x.length)

Returns true if x is defined (x !== undefined)

The opposite of isDef(). Returns true if x === undefined

Reutnrs true if x is an object and the property path specified in propNames exists.

const a = {
    b: {
        c: [0, 1, 2]
    }
}
hasProp(a, 'b', 'c', 0) // returns true
hasProp(a, 'b', 'c', '1') // returns true
hasProp(a, 'b', 'c', 'd') // returns false

Same as hasProp() but only returns true if all prop names are own properties (hence the O in the name). This is the safer way to check the existence of usernames in an object without mistakenly returning true for constructor or other prototypically-inherited properties.

const users = {
    'alex': '123456'
}
const name = 'alex'
hasProp(a, name) // returns true
hasProp(a, 'constructor') // returns true
hasOProp(a, 'constructor') // returns false

Made in Sweden 🇸🇪 by Alex Ewerlöf