HTML

Import:: <script type="text/javascript" src="js/file.js"></script>
Inline:: <script type="text/javascript">alert('Hello World');</script>
Call:: <button id="start" onClick="start()" style="">Start</button>

More Information

Basics

var name;: Initialize a local variable with value undefined
var name = 1;: Initialize variable with value 1
name = 1;: Initialize a global variable with value 1
typeof name: Returns the name of the variables type as string (e.g. "number")
a === b: Checks for value and type equality as opposed to == which only checks for value equality
document.write('Hello World '): Write something to the page
window.location = 'http://www.google.com': Load new url
alert('Hello World'): Open an alert dialog
console.log('Hello World'): Logs to the console in most modern browsers. F12 opens the console in chrome

Math

parseInt(string, base): Returns an integer (base can be 2 for binary, 10 for decimal, 16 for hex, ...)
parseFloat(string): Returns a float (always base 10)
Math.round(num * 100) / 100: Round to two decimal places

Special Types

NaN: Not a number. Gets returned when math operation fail. Use isNaN(value) to check for it because its not possible to check via the == operator
Infinity and -Infinity: Represents an infinite number. Use isFinite(nubmer) to check for it (returns false for NaN too)
undefined: Value of variables that hasn't been assigned yet
null: Placeholder for an object when there is no object

Global functions

decodeURI: TODO
decodeURIComponent: TODO
encodeURI: TODO
encodeURIComponent: TODO
eval: TODO
uneval: TODO

Objects

JavaScript objects are simply collections of name-value pairs. Similar to dictionaries or maps in other languages.

Create an object: var obj = new Object();
or
var obj = {};
Access properties: obj.name = "Simon";
or
var name = obj.name;
or
obj["name"] = "Simon";
or
var name = obj["name"];
Initialize object with properties: var obj = { name: "Carrot", "for": "Max", details: { color: "orange", size: 12 } }

Classes

function Person(first, last) {
    this.first = first;
    this.last = last;
}
Person.prototype.fullName = function() {
    return this.first + ' ' + this.last;
}
Person.prototype.fullNameReversed = function() {
    return this.last + ', ' + this.first;
}

this refers to the object before the .. new creates a new object and binds it to this. For example: s = new Person("Simon", "Willison") s.fullName;

Common methods

obj.hasOwnProperty("prop"): Checks whether this objects contains the property directly. Unlike "prop" in obj it doesn't check the prototype chain
isPrototypeOf: TODO
obj.propertyIsEnumerable("prop"): Checks if the property can be used in a for ... in .. loop
obj.toString() and obj.toLocaleString(): Returns a string representation of the object. Some objects (e.g. Date) take the configured locale (country/language settings) into account
obj.valueOf(): Returns a primitive value for the object. If there is no primitive value the object itself gets returned. Note that this is usually called automatically via a process called autoboxing.

Describe: Prototype chain

Functions

function add(x, y) { var total = x + y; return total; }or anonymous: var add = function(x, y) { var total = x + y; return total; }

Functions implicitly define the array arguments which contains all parameters. These can be more or less than declared in the function header.

func.apply(null, [2, 3, 4, 5]): Calls function using the content of an array as parameters. First parameter is an object or null if it's a simple function
call: TODO

Arrays

JavaScript objects are simply collections of name-value pairs.

Create an array: var a = new Array(); a[0] = "dog"; a[1] = "cat"; a[2] = "hen"; or var a = ["dog", "cat", "hen"];
a.lenhgt: Returns the lenght of the array. This must not be the amount of values since there could be gaps
Loop: for (var i = 0; i < a.length; i++) { //Do something with a[i] } Do not use the following because it will also loop over every property of the array object: ~~for (var i in a) { // Do something with a[i] }~~
a.toString()
a.toLocaleString()
a.concat(item[, itemN]): Returns a new array with the items added on to it.
a.join(sep)
a.pop(): Removes and returns the last item.
a.push(item[, itemN]): Push adds one or more items to the end.
a.reverse(): Reverses the order of the elements in this array. Returns the reversed array.
a.shift()
a.slice(start, end): Returns a sub-array.
a.sort([cmpfn]): Takes an optional comparison function.
a.splice(start, delcount[, itemN]): Lets you modify an array by deleting a section and replacing it with more items.
a.unshift([item])

Javascript