Defined in Module impact.impact


The ig object provides the Module definition and loading capabilities as well as some utility functions. All your code should be wrapped in Modules, so it can be properly loaded and baked.

ig is not an instance of a ig.Class, but just a simple JavaScript object and thus can't be subclassed.

Module Definition


	// code for this module


Define a new Module with a name, requiring all the specified Modules. As soon as all required Modules are loaded, the function passed to .defines() is executed.

If the Module does not require any other Modules, the call to .requires() can be omitted, as in


	// code

The name of a Module directly corresponds to its file location and name. E.g. the file lib/mygame/my-file.js must define a module with the name '', so it can be properly loaded from other Modules.

You can put multiple modules into one file, but be advised, that a module that is referenced from an external file must have it's own file.



Set to true by bake.php to skip the "unresolved dependencies" check when loading modules. The default is false. See Baking.

The currently running ig.Game instance, as created by ig.main() or system.setGame(). If no game has started, is null.

The global context object (same as window when running in a browser)


By default, ig.nocache is an empty string. When the site is loaded with game.html?nocache or ig.setNocache( true ) is called, ig.nocache is set to a random parameter (like '?23478976') to be appended on URLs to bypass the Browser's cache.

This is used by all of Impact's loading functions: Module loading, Images and Sounds.


New in 1.20

The prefix to use for all paths when loading modules files or assets. The default is an empty string.

This value can also be set through the global ImpactPrefix variable before loading Impact. This is, for example, useful if you want to run your game on a page that has a URL of /?page=42, while the game is located in /games/pong/.


<script src="/games/pong/lib/impact/impact.js"></script>
<script src="/games/pong/lib/game/main.js"></script>


The version string of the Impact Game Engine in the form of x.xx

Booleans, indicating if the User Agent is one of the following devices:

New in 1.15

New in 1.22

Main Function

ig.main( canvas, gameClass, fps, width, height, [scale], [loaderClass] );

Initializes ig.system, ig.input, ig.soundManager and and starts the preloader. When the preloader has finished, an instance of gameClass is created at and the run loop is started.

Note that as of 1.20, the fps parameter is ignored in favor of requestAnimationFrame. This allows the browser to decide the best drawing interval, based on the display's refresh rate. If the drawing interval drops below 20hz, the timestep will be capped at 1/20th of a second, essentially slowing the game down. E.g. when only 10 fps can be rendered, an "in game second" takes two "real time seconds". See ig.Timer.maxStep.

Debug Functions

New in 1.18

Impact defines four different functions for debug output: ig.log(), ig.assert() and ig.mark(). However, these functions only actually do something when the Debug Module is loaded. See Debug Messages for details.

It's always safe to call these functions, even when the Debug Module is not loaded.

Utility Functions

ig.$( selector )

Get the DOM-Element(s) from the page according to the given selector. Only element names and IDs are currently supported.

When an Element name is specified (e.g. 'head') an Array of matched elements is returned. When an ID is specified as the selector (e.g. '#canvas') the single Element with this ID is returned.

(This behavior is somewhat inconsistent and might change in future versions)

ig.$new( name )

Create a new DOM-Element with the given name. E.g.:

var audio = ig.$new('Audio');

ig.copy( object )

Returns a deep copy of the given object.

Note that this function can't copy instances of ig.Class or subclasses thereof and just returns them uncopied.

ig.ksort( obj )

Takes an object and returns an Array, sorted by the object properties' keys. E.g.:

var unsorted = { z: 'baz', a: 'bar', b: 'foo' };
var sorted = ig.ksort( unsorted );

sorted[0]; // => bar
sorted[1]; // => foo
sorted[2]; // => baz

ig.merge( target, extended )

Merges all the properties of the extended object recursively into the target object, overwriting existing properties. E.g.:

var settings = { width: 256, height: 128 };
var extendedSettings = { width: 512, foo: 'bar' };

ig.merge( settings, extendedSettings );

settings.width; // => 512
settings.height; // => 128; // => bar

ig.setNocache( set )

When set is true, ig.nocache will be set to a random parameter string. When set is false, ig.nocache will be set to an empty string.

Native JavaScript Object Extensions

Impact extends some of JavaScripts native objects, such as Number, Array and Function. It does not extend Object so you can still safely use for…in loops. fromMin, fromMax, toMin, toMax )

Map a number from a range of values to another range. Numbers are not clamped.

var num = 50; 0, 100, 200, 400 ); // => 300

(50).map( 0, 100, 200, 400 ); // => 300
(25).map( 0, 100, 200, 400 ); // => 250
(150).map( 0, 100, 200, 400 ); // => 500

Number.limit( min, max )

Clamp a number to the range of min and max.

(75).limit( 50, 100 ); // => 75
(25).limit( 50, 100 ); // => 50
(150).limit( 50, 100 ); // => 100

Number.round( [precision] )

Round a number to precision decimal places (default 0).

(3.1415).round(); // => 3
(3.1415).round(2); // => 3.14


Convenience method for Math.floor()


Convenience method for Math.ceil()


Discard decimal places of a number. For negative numbers, the behavior is different to Number.floor().

(2.8).toInt(); // => 2
(-2.8).toInt(); // => -2

(2.8).floor(); // => 2
(-2.8).floor(); // => -3


New in 1.19

Convert radians to degrees

(0.7853981633974483).toDeg(); // => 45


New in 1.19

Convert degrees to radians

(45).toRad(); // => 0.7853981633974483

Array.erase( item )

Find and delete the given item in an array. This method manipulates the array in place.

var a = [4,8,13,15,16,23,42];
a; // => [4,8,15,16,23,42]


Returns a random element from an array.

Function.bind( bind )

Sets the this inside the function to bind. Function.bind() is useful for maintaining the this object for methods used in callbacks.

var foo = {
	bar: 100,
	inc: function() {;
		console.log( );

// Without using bind(), the "this" inside would refer to the 
// "window" instead to itself, when called through setInterval()
setInterval(, 1000 );

Global Modifiers


New in 1.22

If present, the object at ImpactMixin will be merged into the ig namespace before any module loading takes place. This allows you to overwrite Impact's module code to work with different environments (e.g. NodeJS).


<script type="text/javascript">
ImpactMixin = {
	// This function will overwrite Impact's ig.require
	requires: function() {
<script type="text/javascript" src="lib/impact/impact.js"></script>
<script type="text/javascript" src="lib/game/main.js"></script>


If present, this string overwrites ig.prefix.