skrollr.js

/*!
 * skrollr core
 *
 * Alexander Prinzhorn - https://github.com/Prinzhorn/skrollr
 *
 * Free to use under terms of MIT license
 */
(function(window, document, undefined) {
	'use strict';

	/*
	 * Global api.
	 */
	var skrollr = {
		get: function() {
			return _instance;
		},
		//Main entry point.
		init: function(options) {
			return _instance || new Skrollr(options);
		},
		VERSION: '0.6.30'
	};

	//Minify optimization.
	var hasProp = Object.prototype.hasOwnProperty;
	var Math = window.Math;
	var getStyle = window.getComputedStyle;

	//They will be filled when skrollr gets initialized.
	var documentElement;
	var body;

	var EVENT_TOUCHSTART = 'touchstart';
	var EVENT_TOUCHMOVE = 'touchmove';
	var EVENT_TOUCHCANCEL = 'touchcancel';
	var EVENT_TOUCHEND = 'touchend';

	var SKROLLABLE_CLASS = 'skrollable';
	var SKROLLABLE_BEFORE_CLASS = SKROLLABLE_CLASS + '-before';
	var SKROLLABLE_BETWEEN_CLASS = SKROLLABLE_CLASS + '-between';
	var SKROLLABLE_AFTER_CLASS = SKROLLABLE_CLASS + '-after';

	var SKROLLR_CLASS = 'skrollr';
	var NO_SKROLLR_CLASS = 'no-' + SKROLLR_CLASS;
	var SKROLLR_DESKTOP_CLASS = SKROLLR_CLASS + '-desktop';
	var SKROLLR_MOBILE_CLASS = SKROLLR_CLASS + '-mobile';

	var DEFAULT_EASING = 'linear';
	var DEFAULT_DURATION = 1000;//ms
	var DEFAULT_MOBILE_DECELERATION = 0.004;//pixel/ms²

	var DEFAULT_SKROLLRBODY = 'skrollr-body';

	var DEFAULT_SMOOTH_SCROLLING_DURATION = 200;//ms

	var ANCHOR_START = 'start';
	var ANCHOR_END = 'end';
	var ANCHOR_CENTER = 'center';
	var ANCHOR_BOTTOM = 'bottom';

	//The property which will be added to the DOM element to hold the ID of the skrollable.
	var SKROLLABLE_ID_DOM_PROPERTY = '___skrollable_id';

	var rxTouchIgnoreTags = /^(?:input|textarea|button|select)$/i;

	var rxTrim = /^\s+|\s+$/g;

	//Find all data-attributes. data-[_constant]-[offset]-[anchor]-[anchor].
	var rxKeyframeAttribute = /^data(?:-(_\w+))?(?:-?(-?\d*\.?\d+p?))?(?:-?(start|end|top|center|bottom))?(?:-?(top|center|bottom))?$/;

	var rxPropValue = /\s*(@?[\w\-\[\]]+)\s*:\s*(.+?)\s*(?:;|$)/gi;

	//Easing function names follow the property in square brackets.
	var rxPropEasing = /^(@?[a-z\-]+)\[(\w+)\]$/;

	var rxCamelCase = /-([a-z0-9_])/g;
	var rxCamelCaseFn = function(str, letter) {
		return letter.toUpperCase();
	};

	//Numeric values with optional sign.
	var rxNumericValue = /[\-+]?[\d]*\.?[\d]+/g;

	//Used to replace occurences of {?} with a number.
	var rxInterpolateString = /\{\?\}/g;

	//Finds rgb(a) colors, which don't use the percentage notation.
	var rxRGBAIntegerColor = /rgba?\(\s*-?\d+\s*,\s*-?\d+\s*,\s*-?\d+/g;

	//Finds all gradients.
	var rxGradient = /[a-z\-]+-gradient/g;

	//Vendor prefix. Will be set once skrollr gets initialized.
	var theCSSPrefix = '';
	var theDashedCSSPrefix = '';

	//Will be called once (when skrollr gets initialized).
	var detectCSSPrefix = function() {
		//Only relevant prefixes. May be extended.
		//Could be dangerous if there will ever be a CSS property which actually starts with "ms". Don't hope so.
		var rxPrefixes = /^(?:O|Moz|webkit|ms)|(?:-(?:o|moz|webkit|ms)-)/;

		//Detect prefix for current browser by finding the first property using a prefix.
		if(!getStyle) {
			return;
		}

		var style = getStyle(body, null);

		for(var k in style) {
			//We check the key and if the key is a number, we check the value as well, because safari's getComputedStyle returns some weird array-like thingy.
			theCSSPrefix = (k.match(rxPrefixes) || (+k == k && style[k].match(rxPrefixes)));

			if(theCSSPrefix) {
				break;
			}
		}

		//Did we even detect a prefix?
		if(!theCSSPrefix) {
			theCSSPrefix = theDashedCSSPrefix = '';

			return;
		}

		theCSSPrefix = theCSSPrefix[0];

		//We could have detected either a dashed prefix or this camelCaseish-inconsistent stuff.
		if(theCSSPrefix.slice(0,1) === '-') {
			theDashedCSSPrefix = theCSSPrefix;

			//There's no logic behind these. Need a look up.
			theCSSPrefix = ({
				'-webkit-': 'webkit',
				'-moz-': 'Moz',
				'-ms-': 'ms',
				'-o-': 'O'
			})[theCSSPrefix];
		} else {
			theDashedCSSPrefix = '-' + theCSSPrefix.toLowerCase() + '-';
		}
	};

	var polyfillRAF = function() {
		var requestAnimFrame = window.requestAnimationFrame || window[theCSSPrefix.toLowerCase() + 'RequestAnimationFrame'];

		var lastTime = _now();

		if(_isMobile || !requestAnimFrame) {
			requestAnimFrame = function(callback) {
				//How long did it take to render?
				var deltaTime = _now() - lastTime;
				var delay = Math.max(0, 1000 / 60 - deltaTime);

				return window.setTimeout(function() {
					lastTime = _now();
					callback();
				}, delay);
			};
		}

		return requestAnimFrame;
	};

	var polyfillCAF = function() {
		var cancelAnimFrame = window.cancelAnimationFrame || window[theCSSPrefix.toLowerCase() + 'CancelAnimationFrame'];

		if(_isMobile || !cancelAnimFrame) {
			cancelAnimFrame = function(timeout) {
				return window.clearTimeout(timeout);
			};
		}

		return cancelAnimFrame;
	};

	//Built-in easing functions.
	var easings = {
		begin: function() {
			return 0;
		},
		end: function() {
			return 1;
		},
		linear: function(p) {
			return p;
		},
		quadratic: function(p) {
			return p * p;
		},
		cubic: function(p) {
			return p * p * p;
		},
		swing: function(p) {
			return (-Math.cos(p * Math.PI) / 2) + 0.5;
		},
		sqrt: function(p) {
			return Math.sqrt(p);
		},
		outCubic: function(p) {
			return (Math.pow((p - 1), 3) + 1);
		},
		//see https://www.desmos.com/calculator/tbr20s8vd2 for how I did this
		bounce: function(p) {
			var a;

			if(p <= 0.5083) {
				a = 3;
			} else if(p <= 0.8489) {
				a = 9;
			} else if(p <= 0.96208) {
				a = 27;
			} else if(p <= 0.99981) {
				a = 91;
			} else {
				return 1;
			}

			return 1 - Math.abs(3 * Math.cos(p * a * 1.028) / a);
		}
	};

	/**
	 * Constructor.
	 */
	function Skrollr(options) {
		documentElement = document.documentElement;
		body = document.body;

		detectCSSPrefix();

		_instance = this;

		options = options || {};

		_constants = options.constants || {};

		//We allow defining custom easings or overwrite existing.
		if(options.easing) {
			for(var e in options.easing) {
				easings[e] = options.easing[e];
			}
		}

		_edgeStrategy = options.edgeStrategy || 'set';

		_listeners = {
			//Function to be called right before rendering.
			beforerender: options.beforerender,

			//Function to be called right after finishing rendering.
			render: options.render,

			//Function to be called whenever an element with the `data-emit-events` attribute passes a keyframe.
			keyframe: options.keyframe
		};

		//forceHeight is true by default
		_forceHeight = options.forceHeight !== false;

		if(_forceHeight) {
			_scale = options.scale || 1;
		}

		_mobileDeceleration = options.mobileDeceleration || DEFAULT_MOBILE_DECELERATION;

		_smoothScrollingEnabled = options.smoothScrolling !== false;
		_smoothScrollingDuration = options.smoothScrollingDuration || DEFAULT_SMOOTH_SCROLLING_DURATION;

		//Dummy object. Will be overwritten in the _render method when smooth scrolling is calculated.
		_smoothScrolling = {
			targetTop: _instance.getScrollTop()
		};

		//A custom check function may be passed.
		_isMobile = ((options.mobileCheck || function() {
			return (/Android|iPhone|iPad|iPod|BlackBerry/i).test(navigator.userAgent || navigator.vendor || window.opera);
		})());

		if(_isMobile) {
			_skrollrBody = document.getElementById(options.skrollrBody || DEFAULT_SKROLLRBODY);

			//Detect 3d transform if there's a skrollr-body (only needed for #skrollr-body).
			if(_skrollrBody) {
				_detect3DTransforms();
			}

			_initMobile();
			_updateClass(documentElement, [SKROLLR_CLASS, SKROLLR_MOBILE_CLASS], [NO_SKROLLR_CLASS]);
		} else {
			_updateClass(documentElement, [SKROLLR_CLASS, SKROLLR_DESKTOP_CLASS], [NO_SKROLLR_CLASS]);
		}

		//Triggers parsing of elements and a first reflow.
		_instance.refresh();

		_addEvent(window, 'resize orientationchange', function() {
			var width = documentElement.clientWidth;
			var height = documentElement.clientHeight;

			//Only reflow if the size actually changed (#271).
			if(height !== _lastViewportHeight || width !== _lastViewportWidth) {
				_lastViewportHeight = height;
				_lastViewportWidth = width;

				_requestReflow = true;
			}
		});

		var requestAnimFrame = polyfillRAF();

		//Let's go.
		(function animloop(){
			_render();
			_animFrame = requestAnimFrame(animloop);
		}());

		return _instance;
	}

	/**
	 * (Re)parses some or all elements.
	 */
	Skrollr.prototype.refresh = function(elements) {
		var elementIndex;
		var elementsLength;
		var ignoreID = false;

		//Completely reparse anything without argument.
		if(elements === undefined) {
			//Ignore that some elements may already have a skrollable ID.
			ignoreID = true;

			_skrollables = [];
			_skrollableIdCounter = 0;

			elements = document.getElementsByTagName('*');
		} else if(elements.length === undefined) {
			//We also accept a single element as parameter.
			elements = [elements];
		}

		elementIndex = 0;
		elementsLength = elements.length;

		for(; elementIndex < elementsLength; elementIndex++) {
			var el = elements[elementIndex];
			var anchorTarget = el;
			var keyFrames = [];

			//If this particular element should be smooth scrolled.
			var smoothScrollThis = _smoothScrollingEnabled;

			//The edge strategy for this particular element.
			var edgeStrategy = _edgeStrategy;

			//If this particular element should emit keyframe events.
			var emitEvents = false;

			//If we're reseting the counter, remove any old element ids that may be hanging around.
			if(ignoreID && SKROLLABLE_ID_DOM_PROPERTY in el) {
				delete el[SKROLLABLE_ID_DOM_PROPERTY];
			}

			if(!el.attributes) {
				continue;
			}

			//Iterate over all attributes and search for key frame attributes.
			var attributeIndex = 0;
			var attributesLength = el.attributes.length;

			for (; attributeIndex < attributesLength; attributeIndex++) {
				var attr = el.attributes[attributeIndex];

				if(attr.name === 'data-anchor-target') {
					anchorTarget = document.querySelector(attr.value);

					if(anchorTarget === null) {
						throw 'Unable to find anchor target "' + attr.value + '"';
					}

					continue;
				}

				//Global smooth scrolling can be overridden by the element attribute.
				if(attr.name === 'data-smooth-scrolling') {
					smoothScrollThis = attr.value !== 'off';

					continue;
				}

				//Global edge strategy can be overridden by the element attribute.
				if(attr.name === 'data-edge-strategy') {
					edgeStrategy = attr.value;

					continue;
				}

				//Is this element tagged with the `data-emit-events` attribute?
				if(attr.name === 'data-emit-events') {
					emitEvents = true;

					continue;
				}

				var match = attr.name.match(rxKeyframeAttribute);

				if(match === null) {
					continue;
				}

				var kf = {
					props: attr.value,
					//Point back to the element as well.
					element: el,
					//The name of the event which this keyframe will fire, if emitEvents is
					eventType: attr.name.replace(rxCamelCase, rxCamelCaseFn)
				};

				keyFrames.push(kf);

				var constant = match[1];

				if(constant) {
					//Strip the underscore prefix.
					kf.constant = constant.substr(1);
				}

				//Get the key frame offset.
				var offset = match[2];

				//Is it a percentage offset?
				if(/p$/.test(offset)) {
					kf.isPercentage = true;
					kf.offset = (offset.slice(0, -1) | 0) / 100;
				} else {
					kf.offset = (offset | 0);
				}

				var anchor1 = match[3];

				//If second anchor is not set, the first will be taken for both.
				var anchor2 = match[4] || anchor1;

				//"absolute" (or "classic") mode, where numbers mean absolute scroll offset.
				if(!anchor1 || anchor1 === ANCHOR_START || anchor1 === ANCHOR_END) {
					kf.mode = 'absolute';

					//data-end needs to be calculated after all key frames are known.
					if(anchor1 === ANCHOR_END) {
						kf.isEnd = true;
					} else if(!kf.isPercentage) {
						//For data-start we can already set the key frame w/o calculations.
						//#59: "scale" options should only affect absolute mode.
						kf.offset = kf.offset * _scale;
					}
				}
				//"relative" mode, where numbers are relative to anchors.
				else {
					kf.mode = 'relative';
					kf.anchors = [anchor1, anchor2];
				}
			}

			//Does this element have key frames?
			if(!keyFrames.length) {
				continue;
			}

			//Will hold the original style and class attributes before we controlled the element (see #80).
			var styleAttr, classAttr;

			var id;

			if(!ignoreID && SKROLLABLE_ID_DOM_PROPERTY in el) {
				//We already have this element under control. Grab the corresponding skrollable id.
				id = el[SKROLLABLE_ID_DOM_PROPERTY];
				styleAttr = _skrollables[id].styleAttr;
				classAttr = _skrollables[id].classAttr;
			} else {
				//It's an unknown element. Asign it a new skrollable id.
				id = (el[SKROLLABLE_ID_DOM_PROPERTY] = _skrollableIdCounter++);
				styleAttr = el.style.cssText;
				classAttr = _getClass(el);
			}

			_skrollables[id] = {
				element: el,
				styleAttr: styleAttr,
				classAttr: classAttr,
				anchorTarget: anchorTarget,
				keyFrames: keyFrames,
				smoothScrolling: smoothScrollThis,
				edgeStrategy: edgeStrategy,
				emitEvents: emitEvents,
				lastFrameIndex: -1
			};

			_updateClass(el, [SKROLLABLE_CLASS], []);
		}

		//Reflow for the first time.
		_reflow();

		//Now that we got all key frame numbers right, actually parse the properties.
		elementIndex = 0;
		elementsLength = elements.length;

		for(; elementIndex < elementsLength; elementIndex++) {
			var sk = _skrollables[elements[elementIndex][SKROLLABLE_ID_DOM_PROPERTY]];

			if(sk === undefined) {
				continue;
			}

			//Parse the property string to objects
			_parseProps(sk);

			//Fill key frames with missing properties from left and right
			_fillProps(sk);
		}

		return _instance;
	};

	/**
	 * Transform "relative" mode to "absolute" mode.
	 * That is, calculate anchor position and offset of element.
	 */
	Skrollr.prototype.relativeToAbsolute = function(element, viewportAnchor, elementAnchor) {
		var viewportHeight = documentElement.clientHeight;
		var box = element.getBoundingClientRect();
		var absolute = box.top;

		//#100: IE doesn't supply "height" with getBoundingClientRect.
		var boxHeight = box.bottom - box.top;

		if(viewportAnchor === ANCHOR_BOTTOM) {
			absolute -= viewportHeight;
		} else if(viewportAnchor === ANCHOR_CENTER) {
			absolute -= viewportHeight / 2;
		}

		if(elementAnchor === ANCHOR_BOTTOM) {
			absolute += boxHeight;
		} else if(elementAnchor === ANCHOR_CENTER) {
			absolute += boxHeight / 2;
		}

		//Compensate scrolling since getBoundingClientRect is relative to viewport.
		absolute += _instance.getScrollTop();

		return (absolute + 0.5) | 0;
	};

	/**
	 * Animates scroll top to new position.
	 */
	Skrollr.prototype.animateTo = function(top, options) {
		options = options || {};

		var now = _now();
		var scrollTop = _instance.getScrollTop();
		var duration = options.duration === undefined ? DEFAULT_DURATION : options.duration;

		//Setting this to a new value will automatically cause the current animation to stop, if any.
		_scrollAnimation = {
			startTop: scrollTop,
			topDiff: top - scrollTop,
			targetTop: top,
			duration: duration,
			startTime: now,
			endTime: now + duration,
			easing: easings[options.easing || DEFAULT_EASING],
			done: options.done
		};

		//Don't queue the animation if there's nothing to animate.
		if(!_scrollAnimation.topDiff) {
			if(_scrollAnimation.done) {
				_scrollAnimation.done.call(_instance, false);
			}

			_scrollAnimation = undefined;
		}

		return _instance;
	};

	/**
	 * Stops animateTo animation.
	 */
	Skrollr.prototype.stopAnimateTo = function() {
		if(_scrollAnimation && _scrollAnimation.done) {
			_scrollAnimation.done.call(_instance, true);
		}

		_scrollAnimation = undefined;
	};

	/**
	 * Returns if an animation caused by animateTo is currently running.
	 */
	Skrollr.prototype.isAnimatingTo = function() {
		return !!_scrollAnimation;
	};

	Skrollr.prototype.isMobile = function() {
		return _isMobile;
	};

	Skrollr.prototype.setScrollTop = function(top, force) {
		_forceRender = (force === true);

		if(_isMobile) {
			_mobileOffset = Math.min(Math.max(top, 0), _maxKeyFrame);
		} else {
			window.scrollTo(0, top);
		}

		return _instance;
	};

	Skrollr.prototype.getScrollTop = function() {
		if(_isMobile) {
			return _mobileOffset;
		} else {
			return window.pageYOffset || documentElement.scrollTop || body.scrollTop || 0;
		}
	};

	Skrollr.prototype.getMaxScrollTop = function() {
		return _maxKeyFrame;
	};

	Skrollr.prototype.on = function(name, fn) {
		_listeners[name] = fn;

		return _instance;
	};

	Skrollr.prototype.off = function(name) {
		delete _listeners[name];

		return _instance;
	};

	Skrollr.prototype.destroy = function() {
		var cancelAnimFrame = polyfillCAF();
		cancelAnimFrame(_animFrame);
		_removeAllEvents();

		_updateClass(documentElement, [NO_SKROLLR_CLASS], [SKROLLR_CLASS, SKROLLR_DESKTOP_CLASS, SKROLLR_MOBILE_CLASS]);

		var skrollableIndex = 0;
		var skrollablesLength = _skrollables.length;

		for(; skrollableIndex < skrollablesLength; skrollableIndex++) {
			_reset(_skrollables[skrollableIndex].element);
		}

		documentElement.style.overflow = body.style.overflow = '';
		documentElement.style.height = body.style.height = '';

		if(_skrollrBody) {
			skrollr.setStyle(_skrollrBody, 'transform', 'none');
		}

		_instance = undefined;
		_skrollrBody = undefined;
		_listeners = undefined;
		_forceHeight = undefined;
		_maxKeyFrame = 0;
		_scale = 1;
		_constants = undefined;
		_mobileDeceleration = undefined;
		_direction = 'down';
		_lastTop = -1;
		_lastViewportWidth = 0;
		_lastViewportHeight = 0;
		_requestReflow = false;
		_scrollAnimation = undefined;
		_smoothScrollingEnabled = undefined;
		_smoothScrollingDuration = undefined;
		_smoothScrolling = undefined;
		_forceRender = undefined;
		_skrollableIdCounter = 0;
		_edgeStrategy = undefined;
		_isMobile = false;
		_mobileOffset = 0;
		_translateZ = undefined;
	};

	/*
		Private methods.
	*/

	var _initMobile = function() {
		var initialElement;
		var initialTouchY;
		var initialTouchX;
		var currentElement;
		var currentTouchY;
		var currentTouchX;
		var lastTouchY;
		var deltaY;

		var initialTouchTime;
		var currentTouchTime;
		var lastTouchTime;
		var deltaTime;

		_addEvent(documentElement, [EVENT_TOUCHSTART, EVENT_TOUCHMOVE, EVENT_TOUCHCANCEL, EVENT_TOUCHEND].join(' '), function(e) {
			var touch = e.changedTouches[0];

			currentElement = e.target;

			//We don't want text nodes.
			while(currentElement.nodeType === 3) {
				currentElement = currentElement.parentNode;
			}

			currentTouchY = touch.clientY;
			currentTouchX = touch.clientX;
			currentTouchTime = e.timeStamp;

			if(!rxTouchIgnoreTags.test(currentElement.tagName)) {
				e.preventDefault();
			}

			switch(e.type) {
				case EVENT_TOUCHSTART:
					//The last element we tapped on.
					if(initialElement) {
						initialElement.blur();
					}

					_instance.stopAnimateTo();

					initialElement = currentElement;

					initialTouchY = lastTouchY = currentTouchY;
					initialTouchX = currentTouchX;
					initialTouchTime = currentTouchTime;

					break;
				case EVENT_TOUCHMOVE:
					//Prevent default event on touchIgnore elements in case they don't have focus yet.
					if(rxTouchIgnoreTags.test(currentElement.tagName) && document.activeElement !== currentElement) {
						e.preventDefault();
					}

					deltaY = currentTouchY - lastTouchY;
					deltaTime = currentTouchTime - lastTouchTime;

					_instance.setScrollTop(_mobileOffset - deltaY, true);

					lastTouchY = currentTouchY;
					lastTouchTime = currentTouchTime;
					break;
				default:
				case EVENT_TOUCHCANCEL:
				case EVENT_TOUCHEND:
					var distanceY = initialTouchY - currentTouchY;
					var distanceX = initialTouchX - currentTouchX;
					var distance2 = distanceX * distanceX + distanceY * distanceY;

					//Check if it was more like a tap (moved less than 7px).
					if(distance2 < 49) {
						if(!rxTouchIgnoreTags.test(initialElement.tagName)) {
							initialElement.focus();

							//It was a tap, click the element.
							var clickEvent = document.createEvent('MouseEvents');
							clickEvent.initMouseEvent('click', true, true, e.view, 1, touch.screenX, touch.screenY, touch.clientX, touch.clientY, e.ctrlKey, e.altKey, e.shiftKey, e.metaKey, 0, null);
							initialElement.dispatchEvent(clickEvent);
						}

						return;
					}

					initialElement = undefined;

					var speed = deltaY / deltaTime;

					//Cap speed at 3 pixel/ms.
					speed = Math.max(Math.min(speed, 3), -3);

					var duration = Math.abs(speed / _mobileDeceleration);
					var targetOffset = speed * duration + 0.5 * _mobileDeceleration * duration * duration;
					var targetTop = _instance.getScrollTop() - targetOffset;

					//Relative duration change for when scrolling above bounds.
					var targetRatio = 0;

					//Change duration proportionally when scrolling would leave bounds.
					if(targetTop > _maxKeyFrame) {
						targetRatio = (_maxKeyFrame - targetTop) / targetOffset;

						targetTop = _maxKeyFrame;
					} else if(targetTop < 0) {
						targetRatio = -targetTop / targetOffset;

						targetTop = 0;
					}

					duration = duration * (1 - targetRatio);

					_instance.animateTo((targetTop + 0.5) | 0, {easing: 'outCubic', duration: duration});
					break;
			}
		});

		//Just in case there has already been some native scrolling, reset it.
		window.scrollTo(0, 0);
		documentElement.style.overflow = body.style.overflow = 'hidden';
	};

	/**
	 * Updates key frames which depend on others / need to be updated on resize.
	 * That is "end" in "absolute" mode and all key frames in "relative" mode.
	 * Also handles constants, because they may change on resize.
	 */
	var _updateDependentKeyFrames = function() {
		var viewportHeight = documentElement.clientHeight;
		var processedConstants = _processConstants();
		var skrollable;
		var element;
		var anchorTarget;
		var keyFrames;
		var keyFrameIndex;
		var keyFramesLength;
		var kf;
		var skrollableIndex;
		var skrollablesLength;
		var offset;
		var constantValue;

		//First process all relative-mode elements and find the max key frame.
		skrollableIndex = 0;
		skrollablesLength = _skrollables.length;

		for(; skrollableIndex < skrollablesLength; skrollableIndex++) {
			skrollable = _skrollables[skrollableIndex];
			element = skrollable.element;
			anchorTarget = skrollable.anchorTarget;
			keyFrames = skrollable.keyFrames;

			keyFrameIndex = 0;
			keyFramesLength = keyFrames.length;

			for(; keyFrameIndex < keyFramesLength; keyFrameIndex++) {
				kf = keyFrames[keyFrameIndex];

				offset = kf.offset;
				constantValue = processedConstants[kf.constant] || 0;

				kf.frame = offset;

				if(kf.isPercentage) {
					//Convert the offset to percentage of the viewport height.
					offset = offset * viewportHeight;

					//Absolute + percentage mode.
					kf.frame = offset;
				}

				if(kf.mode === 'relative') {
					_reset(element);

					kf.frame = _instance.relativeToAbsolute(anchorTarget, kf.anchors[0], kf.anchors[1]) - offset;

					_reset(element, true);
				}

				kf.frame += constantValue;

				//Only search for max key frame when forceHeight is enabled.
				if(_forceHeight) {
					//Find the max key frame, but don't use one of the data-end ones for comparison.
					if(!kf.isEnd && kf.frame > _maxKeyFrame) {
						_maxKeyFrame = kf.frame;
					}
				}
			}
		}

		//#133: The document can be larger than the maxKeyFrame we found.
		_maxKeyFrame = Math.max(_maxKeyFrame, _getDocumentHeight());

		//Now process all data-end keyframes.
		skrollableIndex = 0;
		skrollablesLength = _skrollables.length;

		for(; skrollableIndex < skrollablesLength; skrollableIndex++) {
			skrollable = _skrollables[skrollableIndex];
			keyFrames = skrollable.keyFrames;

			keyFrameIndex = 0;
			keyFramesLength = keyFrames.length;

			for(; keyFrameIndex < keyFramesLength; keyFrameIndex++) {
				kf = keyFrames[keyFrameIndex];

				constantValue = processedConstants[kf.constant] || 0;

				if(kf.isEnd) {
					kf.frame = _maxKeyFrame - kf.offset + constantValue;
				}
			}

			skrollable.keyFrames.sort(_keyFrameComparator);
		}
	};

	/**
	 * Calculates and sets the style properties for the element at the given frame.
	 * @param fakeFrame The frame to render at when smooth scrolling is enabled.
	 * @param actualFrame The actual frame we are at.
	 */
	var _calcSteps = function(fakeFrame, actualFrame) {
		//Iterate over all skrollables.
		var skrollableIndex = 0;
		var skrollablesLength = _skrollables.length;

		for(; skrollableIndex < skrollablesLength; skrollableIndex++) {
			var skrollable = _skrollables[skrollableIndex];
			var element = skrollable.element;
			var frame = skrollable.smoothScrolling ? fakeFrame : actualFrame;
			var frames = skrollable.keyFrames;
			var framesLength = frames.length;
			var firstFrame = frames[0];
			var lastFrame = frames[frames.length - 1];
			var beforeFirst = frame < firstFrame.frame;
			var afterLast = frame > lastFrame.frame;
			var firstOrLastFrame = beforeFirst ? firstFrame : lastFrame;
			var emitEvents = skrollable.emitEvents;
			var lastFrameIndex = skrollable.lastFrameIndex;
			var key;
			var value;

			//If we are before/after the first/last frame, set the styles according to the given edge strategy.
			if(beforeFirst || afterLast) {
				//Check if we already handled this edge case last time.
				//Note: using setScrollTop it's possible that we jumped from one edge to the other.
				if(beforeFirst && skrollable.edge === -1 || afterLast && skrollable.edge === 1) {
					continue;
				}

				//Add the skrollr-before or -after class.
				if(beforeFirst) {
					_updateClass(element, [SKROLLABLE_BEFORE_CLASS], [SKROLLABLE_AFTER_CLASS, SKROLLABLE_BETWEEN_CLASS]);

					//This handles the special case where we exit the first keyframe.
					if(emitEvents && lastFrameIndex > -1) {
						_emitEvent(element, firstFrame.eventType, _direction);
						skrollable.lastFrameIndex = -1;
					}
				} else {
					_updateClass(element, [SKROLLABLE_AFTER_CLASS], [SKROLLABLE_BEFORE_CLASS, SKROLLABLE_BETWEEN_CLASS]);

					//This handles the special case where we exit the last keyframe.
					if(emitEvents && lastFrameIndex < framesLength) {
						_emitEvent(element, lastFrame.eventType, _direction);
						skrollable.lastFrameIndex = framesLength;
					}
				}

				//Remember that we handled the edge case (before/after the first/last keyframe).
				skrollable.edge = beforeFirst ? -1 : 1;

				switch(skrollable.edgeStrategy) {
					case 'reset':
						_reset(element);
						continue;
					case 'ease':
						//Handle this case like it would be exactly at first/last keyframe and just pass it on.
						frame = firstOrLastFrame.frame;
						break;
					default:
					case 'set':
						var props = firstOrLastFrame.props;

						for(key in props) {
							if(hasProp.call(props, key)) {
								value = _interpolateString(props[key].value);

								//Set style or attribute.
								if(key.indexOf('@') === 0) {
									element.setAttribute(key.substr(1), value);
								} else {
									skrollr.setStyle(element, key, value);
								}
							}
						}

						continue;
				}
			} else {
				//Did we handle an edge last time?
				if(skrollable.edge !== 0) {
					_updateClass(element, [SKROLLABLE_CLASS, SKROLLABLE_BETWEEN_CLASS], [SKROLLABLE_BEFORE_CLASS, SKROLLABLE_AFTER_CLASS]);
					skrollable.edge = 0;
				}
			}

			//Find out between which two key frames we are right now.
			var keyFrameIndex = 0;

			for(; keyFrameIndex < framesLength - 1; keyFrameIndex++) {
				if(frame >= frames[keyFrameIndex].frame && frame <= frames[keyFrameIndex + 1].frame) {
					var left = frames[keyFrameIndex];
					var right = frames[keyFrameIndex + 1];

					for(key in left.props) {
						if(hasProp.call(left.props, key)) {
							var progress = (frame - left.frame) / (right.frame - left.frame);

							//Transform the current progress using the given easing function.
							progress = left.props[key].easing(progress);

							//Interpolate between the two values
							value = _calcInterpolation(left.props[key].value, right.props[key].value, progress);

							value = _interpolateString(value);

							//Set style or attribute.
							if(key.indexOf('@') === 0) {
								element.setAttribute(key.substr(1), value);
							} else {
								skrollr.setStyle(element, key, value);
							}
						}
					}

					//Are events enabled on this element?
					//This code handles the usual cases of scrolling through different keyframes.
					//The special cases of before first and after last keyframe are handled above.
					if(emitEvents) {
						//Did we pass a new keyframe?
						if(lastFrameIndex !== keyFrameIndex) {
							if(_direction === 'down') {
								_emitEvent(element, left.eventType, _direction);
							} else {
								_emitEvent(element, right.eventType, _direction);
							}

							skrollable.lastFrameIndex = keyFrameIndex;
						}
					}

					break;
				}
			}
		}
	};

	/**
	 * Renders all elements.
	 */
	var _render = function() {
		if(_requestReflow) {
			_requestReflow = false;
			_reflow();
		}

		//We may render something else than the actual scrollbar position.
		var renderTop = _instance.getScrollTop();

		//If there's an animation, which ends in current render call, call the callback after rendering.
		var afterAnimationCallback;
		var now = _now();
		var progress;

		//Before actually rendering handle the scroll animation, if any.
		if(_scrollAnimation) {
			//It's over
			if(now >= _scrollAnimation.endTime) {
				renderTop = _scrollAnimation.targetTop;
				afterAnimationCallback = _scrollAnimation.done;
				_scrollAnimation = undefined;
			} else {
				//Map the current progress to the new progress using given easing function.
				progress = _scrollAnimation.easing((now - _scrollAnimation.startTime) / _scrollAnimation.duration);

				renderTop = (_scrollAnimation.startTop + progress * _scrollAnimation.topDiff) | 0;
			}

			_instance.setScrollTop(renderTop, true);
		}
		//Smooth scrolling only if there's no animation running and if we're not forcing the rendering.
		else if(!_forceRender) {
			var smoothScrollingDiff = _smoothScrolling.targetTop - renderTop;

			//The user scrolled, start new smooth scrolling.
			if(smoothScrollingDiff) {
				_smoothScrolling = {
					startTop: _lastTop,
					topDiff: renderTop - _lastTop,
					targetTop: renderTop,
					startTime: _lastRenderCall,
					endTime: _lastRenderCall + _smoothScrollingDuration
				};
			}

			//Interpolate the internal scroll position (not the actual scrollbar).
			if(now <= _smoothScrolling.endTime) {
				//Map the current progress to the new progress using easing function.
				progress = easings.sqrt((now - _smoothScrolling.startTime) / _smoothScrollingDuration);

				renderTop = (_smoothScrolling.startTop + progress * _smoothScrolling.topDiff) | 0;
			}
		}

		//Did the scroll position even change?
		if(_forceRender || _lastTop !== renderTop) {
			//Remember in which direction are we scrolling?
			_direction = (renderTop > _lastTop) ? 'down' : (renderTop < _lastTop ? 'up' : _direction);

			_forceRender = false;

			var listenerParams = {
				curTop: renderTop,
				lastTop: _lastTop,
				maxTop: _maxKeyFrame,
				direction: _direction
			};

			//Tell the listener we are about to render.
			var continueRendering = _listeners.beforerender && _listeners.beforerender.call(_instance, listenerParams);

			//The beforerender listener function is able the cancel rendering.
			if(continueRendering !== false) {
				//Now actually interpolate all the styles.
				_calcSteps(renderTop, _instance.getScrollTop());

				//That's were we actually "scroll" on mobile.
				if(_isMobile && _skrollrBody) {
					//Set the transform ("scroll it").
					skrollr.setStyle(_skrollrBody, 'transform', 'translate(0, ' + -(_mobileOffset) + 'px) ' + _translateZ);
				}

				//Remember when we last rendered.
				_lastTop = renderTop;

				if(_listeners.render) {
					_listeners.render.call(_instance, listenerParams);
				}
			}

			if(afterAnimationCallback) {
				afterAnimationCallback.call(_instance, false);
			}
		}

		_lastRenderCall = now;
	};

	/**
	 * Parses the properties for each key frame of the given skrollable.
	 */
	var _parseProps = function(skrollable) {
		//Iterate over all key frames
		var keyFrameIndex = 0;
		var keyFramesLength = skrollable.keyFrames.length;

		for(; keyFrameIndex < keyFramesLength; keyFrameIndex++) {
			var frame = skrollable.keyFrames[keyFrameIndex];
			var easing;
			var value;
			var prop;
			var props = {};

			var match;

			while((match = rxPropValue.exec(frame.props)) !== null) {
				prop = match[1];
				value = match[2];

				easing = prop.match(rxPropEasing);

				//Is there an easing specified for this prop?
				if(easing !== null) {
					prop = easing[1];
					easing = easing[2];
				} else {
					easing = DEFAULT_EASING;
				}

				//Exclamation point at first position forces the value to be taken literal.
				value = value.indexOf('!') ? _parseProp(value) : [value.slice(1)];

				//Save the prop for this key frame with his value and easing function
				props[prop] = {
					value: value,
					easing: easings[easing]
				};
			}

			frame.props = props;
		}
	};

	/**
	 * Parses a value extracting numeric values and generating a format string
	 * for later interpolation of the new values in old string.
	 *
	 * @param val The CSS value to be parsed.
	 * @return Something like ["rgba(?%,?%, ?%,?)", 100, 50, 0, .7]
	 * where the first element is the format string later used
	 * and all following elements are the numeric value.
	 */
	var _parseProp = function(val) {
		var numbers = [];

		//One special case, where floats don't work.
		//We replace all occurences of rgba colors
		//which don't use percentage notation with the percentage notation.
		rxRGBAIntegerColor.lastIndex = 0;
		val = val.replace(rxRGBAIntegerColor, function(rgba) {
			return rgba.replace(rxNumericValue, function(n) {
				return n / 255 * 100 + '%';
			});
		});

		//Handle prefixing of "gradient" values.
		//For now only the prefixed value will be set. Unprefixed isn't supported anyway.
		if(theDashedCSSPrefix) {
			rxGradient.lastIndex = 0;
			val = val.replace(rxGradient, function(s) {
				return theDashedCSSPrefix + s;
			});
		}

		//Now parse ANY number inside this string and create a format string.
		val = val.replace(rxNumericValue, function(n) {
			numbers.push(+n);
			return '{?}';
		});

		//Add the formatstring as first value.
		numbers.unshift(val);

		return numbers;
	};

	/**
	 * Fills the key frames with missing left and right hand properties.
	 * If key frame 1 has property X and key frame 2 is missing X,
	 * but key frame 3 has X again, then we need to assign X to key frame 2 too.
	 *
	 * @param sk A skrollable.
	 */
	var _fillProps = function(sk) {
		//Will collect the properties key frame by key frame
		var propList = {};
		var keyFrameIndex;
		var keyFramesLength;

		//Iterate over all key frames from left to right
		keyFrameIndex = 0;
		keyFramesLength = sk.keyFrames.length;

		for(; keyFrameIndex < keyFramesLength; keyFrameIndex++) {
			_fillPropForFrame(sk.keyFrames[keyFrameIndex], propList);
		}

		//Now do the same from right to fill the last gaps

		propList = {};

		//Iterate over all key frames from right to left
		keyFrameIndex = sk.keyFrames.length - 1;

		for(; keyFrameIndex >= 0; keyFrameIndex--) {
			_fillPropForFrame(sk.keyFrames[keyFrameIndex], propList);
		}
	};

	var _fillPropForFrame = function(frame, propList) {
		var key;

		//For each key frame iterate over all right hand properties and assign them,
		//but only if the current key frame doesn't have the property by itself
		for(key in propList) {
			//The current frame misses this property, so assign it.
			if(!hasProp.call(frame.props, key)) {
				frame.props[key] = propList[key];
			}
		}

		//Iterate over all props of the current frame and collect them
		for(key in frame.props) {
			propList[key] = frame.props[key];
		}
	};

	/**
	 * Calculates the new values for two given values array.
	 */
	var _calcInterpolation = function(val1, val2, progress) {
		var valueIndex;
		var val1Length = val1.length;

		//They both need to have the same length
		if(val1Length !== val2.length) {
			throw 'Can\'t interpolate between "' + val1[0] + '" and "' + val2[0] + '"';
		}

		//Add the format string as first element.
		var interpolated = [val1[0]];

		valueIndex = 1;

		for(; valueIndex < val1Length; valueIndex++) {
			//That's the line where the two numbers are actually interpolated.
			interpolated[valueIndex] = val1[valueIndex] + ((val2[valueIndex] - val1[valueIndex]) * progress);
		}

		return interpolated;
	};

	/**
	 * Interpolates the numeric values into the format string.
	 */
	var _interpolateString = function(val) {
		var valueIndex = 1;

		rxInterpolateString.lastIndex = 0;

		return val[0].replace(rxInterpolateString, function() {
			return val[valueIndex++];
		});
	};

	/**
	 * Resets the class and style attribute to what it was before skrollr manipulated the element.
	 * Also remembers the values it had before reseting, in order to undo the reset.
	 */
	var _reset = function(elements, undo) {
		//We accept a single element or an array of elements.
		elements = [].concat(elements);

		var skrollable;
		var element;
		var elementsIndex = 0;
		var elementsLength = elements.length;

		for(; elementsIndex < elementsLength; elementsIndex++) {
			element = elements[elementsIndex];
			skrollable = _skrollables[element[SKROLLABLE_ID_DOM_PROPERTY]];

			//Couldn't find the skrollable for this DOM element.
			if(!skrollable) {
				continue;
			}

			if(undo) {
				//Reset class and style to the "dirty" (set by skrollr) values.
				element.style.cssText = skrollable.dirtyStyleAttr;
				_updateClass(element, skrollable.dirtyClassAttr);
			} else {
				//Remember the "dirty" (set by skrollr) class and style.
				skrollable.dirtyStyleAttr = element.style.cssText;
				skrollable.dirtyClassAttr = _getClass(element);

				//Reset class and style to what it originally was.
				element.style.cssText = skrollable.styleAttr;
				_updateClass(element, skrollable.classAttr);
			}
		}
	};

	/**
	 * Detects support for 3d transforms by applying it to the skrollr-body.
	 */
	var _detect3DTransforms = function() {
		_translateZ = 'translateZ(0)';
		skrollr.setStyle(_skrollrBody, 'transform', _translateZ);

		var computedStyle = getStyle(_skrollrBody);
		var computedTransform = computedStyle.getPropertyValue('transform');
		var computedTransformWithPrefix = computedStyle.getPropertyValue(theDashedCSSPrefix + 'transform');
		var has3D = (computedTransform && computedTransform !== 'none') || (computedTransformWithPrefix && computedTransformWithPrefix !== 'none');

		if(!has3D) {
			_translateZ = '';
		}
	};

	/**
	 * Set the CSS property on the given element. Sets prefixed properties as well.
	 */
	skrollr.setStyle = function(el, prop, val) {
		var style = el.style;

		//Camel case.
		prop = prop.replace(rxCamelCase, rxCamelCaseFn).replace('-', '');

		//Make sure z-index gets a <integer>.
		//This is the only <integer> case we need to handle.
		if(prop === 'zIndex') {
			if(isNaN(val)) {
				//If it's not a number, don't touch it.
				//It could for example be "auto" (#351).
				style[prop] = val;
			} else {
				//Floor the number.
				style[prop] = '' + (val | 0);
			}
		}
		//#64: "float" can't be set across browsers. Needs to use "cssFloat" for all except IE.
		else if(prop === 'float') {
			style.styleFloat = style.cssFloat = val;
		}
		else {
			//Need try-catch for old IE.
			try {
				//Set prefixed property if there's a prefix.
				if(theCSSPrefix) {
					style[theCSSPrefix + prop.slice(0,1).toUpperCase() + prop.slice(1)] = val;
				}

				//Set unprefixed.
				style[prop] = val;
			} catch(ignore) {}
		}
	};

	/**
	 * Cross browser event handling.
	 */
	var _addEvent = skrollr.addEvent = function(element, names, callback) {
		var intermediate = function(e) {
			//Normalize IE event stuff.
			e = e || window.event;

			if(!e.target) {
				e.target = e.srcElement;
			}

			if(!e.preventDefault) {
				e.preventDefault = function() {
					e.returnValue = false;
					e.defaultPrevented = true;
				};
			}

			return callback.call(this, e);
		};

		names = names.split(' ');

		var name;
		var nameCounter = 0;
		var namesLength = names.length;

		for(; nameCounter < namesLength; nameCounter++) {
			name = names[nameCounter];

			if(element.addEventListener) {
				element.addEventListener(name, callback, false);
			} else {
				element.attachEvent('on' + name, intermediate);
			}

			//Remember the events to be able to flush them later.
			_registeredEvents.push({
				element: element,
				name: name,
				listener: callback
			});
		}
	};

	var _removeEvent = skrollr.removeEvent = function(element, names, callback) {
		names = names.split(' ');

		var nameCounter = 0;
		var namesLength = names.length;

		for(; nameCounter < namesLength; nameCounter++) {
			if(element.removeEventListener) {
				element.removeEventListener(names[nameCounter], callback, false);
			} else {
				element.detachEvent('on' + names[nameCounter], callback);
			}
		}
	};

	var _removeAllEvents = function() {
		var eventData;
		var eventCounter = 0;
		var eventsLength = _registeredEvents.length;

		for(; eventCounter < eventsLength; eventCounter++) {
			eventData = _registeredEvents[eventCounter];

			_removeEvent(eventData.element, eventData.name, eventData.listener);
		}

		_registeredEvents = [];
	};

	var _emitEvent = function(element, name, direction) {
		if(_listeners.keyframe) {
			_listeners.keyframe.call(_instance, element, name, direction);
		}
	};

	var _reflow = function() {
		var pos = _instance.getScrollTop();

		//Will be recalculated by _updateDependentKeyFrames.
		_maxKeyFrame = 0;

		if(_forceHeight && !_isMobile) {
			//un-"force" the height to not mess with the calculations in _updateDependentKeyFrames (#216).
			body.style.height = '';
		}

		_updateDependentKeyFrames();

		if(_forceHeight && !_isMobile) {
			//"force" the height.
			body.style.height = (_maxKeyFrame + documentElement.clientHeight) + 'px';
		}

		//The scroll offset may now be larger than needed (on desktop the browser/os prevents scrolling farther than the bottom).
		if(_isMobile) {
			_instance.setScrollTop(Math.min(_instance.getScrollTop(), _maxKeyFrame));
		} else {
			//Remember and reset the scroll pos (#217).
			_instance.setScrollTop(pos, true);
		}

		_forceRender = true;
	};

	/*
	 * Returns a copy of the constants object where all functions and strings have been evaluated.
	 */
	var _processConstants = function() {
		var viewportHeight = documentElement.clientHeight;
		var copy = {};
		var prop;
		var value;

		for(prop in _constants) {
			value = _constants[prop];

			if(typeof value === 'function') {
				value = value.call(_instance);
			}
			//Percentage offset.
			else if((/p$/).test(value)) {
				value = (value.slice(0, -1) / 100) * viewportHeight;
			}

			copy[prop] = value;
		}

		return copy;
	};

	/*
	 * Returns the height of the document.
	 */
	var _getDocumentHeight = function() {
		var skrollrBodyHeight = 0;
		var bodyHeight;

		if(_skrollrBody) {
			skrollrBodyHeight = Math.max(_skrollrBody.offsetHeight, _skrollrBody.scrollHeight);
		}

		bodyHeight = Math.max(skrollrBodyHeight, body.scrollHeight, body.offsetHeight, documentElement.scrollHeight, documentElement.offsetHeight, documentElement.clientHeight);

		return bodyHeight - documentElement.clientHeight;
	};

	/**
	 * Returns a string of space separated classnames for the current element.
	 * Works with SVG as well.
	 */
	var _getClass = function(element) {
		var prop = 'className';

		//SVG support by using className.baseVal instead of just className.
		if(window.SVGElement && element instanceof window.SVGElement) {
			element = element[prop];
			prop = 'baseVal';
		}

		return element[prop];
	};

	/**
	 * Adds and removes a CSS classes.
	 * Works with SVG as well.
	 * add and remove are arrays of strings,
	 * or if remove is ommited add is a string and overwrites all classes.
	 */
	var _updateClass = function(element, add, remove) {
		var prop = 'className';

		//SVG support by using className.baseVal instead of just className.
		if(window.SVGElement && element instanceof window.SVGElement) {
			element = element[prop];
			prop = 'baseVal';
		}

		//When remove is ommited, we want to overwrite/set the classes.
		if(remove === undefined) {
			element[prop] = add;
			return;
		}

		//Cache current classes. We will work on a string before passing back to DOM.
		var val = element[prop];

		//All classes to be removed.
		var classRemoveIndex = 0;
		var removeLength = remove.length;

		for(; classRemoveIndex < removeLength; classRemoveIndex++) {
			val = _untrim(val).replace(_untrim(remove[classRemoveIndex]), ' ');
		}

		val = _trim(val);

		//All classes to be added.
		var classAddIndex = 0;
		var addLength = add.length;

		for(; classAddIndex < addLength; classAddIndex++) {
			//Only add if el not already has class.
			if(_untrim(val).indexOf(_untrim(add[classAddIndex])) === -1) {
				val += ' ' + add[classAddIndex];
			}
		}

		element[prop] = _trim(val);
	};

	var _trim = function(a) {
		return a.replace(rxTrim, '');
	};

	/**
	 * Adds a space before and after the string.
	 */
	var _untrim = function(a) {
		return ' ' + a + ' ';
	};

	var _now = Date.now || function() {
		return +new Date();
	};

	var _keyFrameComparator = function(a, b) {
		return a.frame - b.frame;
	};

	/*
	 * Private variables.
	 */

	//Singleton
	var _instance;

	/*
		A list of all elements which should be animated associated with their the metadata.
		Exmaple skrollable with two key frames animating from 100px width to 20px:

		skrollable = {
			element: <the DOM element>,
			styleAttr: <style attribute of the element before skrollr>,
			classAttr: <class attribute of the element before skrollr>,
			keyFrames: [
				{
					frame: 100,
					props: {
						width: {
							value: ['{?}px', 100],
							easing: <reference to easing function>
						}
					},
					mode: "absolute"
				},
				{
					frame: 200,
					props: {
						width: {
							value: ['{?}px', 20],
							easing: <reference to easing function>
						}
					},
					mode: "absolute"
				}
			]
		};
	*/
	var _skrollables;

	var _skrollrBody;

	var _listeners;
	var _forceHeight;
	var _maxKeyFrame = 0;

	var _scale = 1;
	var _constants;

	var _mobileDeceleration;

	//Current direction (up/down).
	var _direction = 'down';

	//The last top offset value. Needed to determine direction.
	var _lastTop = -1;

	//The last time we called the render method (doesn't mean we rendered!).
	var _lastRenderCall = _now();

	//For detecting if it actually resized (#271).
	var _lastViewportWidth = 0;
	var _lastViewportHeight = 0;

	var _requestReflow = false;

	//Will contain data about a running scrollbar animation, if any.
	var _scrollAnimation;

	var _smoothScrollingEnabled;

	var _smoothScrollingDuration;

	//Will contain settins for smooth scrolling if enabled.
	var _smoothScrolling;

	//Can be set by any operation/event to force rendering even if the scrollbar didn't move.
	var _forceRender;

	//Each skrollable gets an unique ID incremented for each skrollable.
	//The ID is the index in the _skrollables array.
	var _skrollableIdCounter = 0;

	var _edgeStrategy;


	//Mobile specific vars. Will be stripped by UglifyJS when not in use.
	var _isMobile = false;

	//The virtual scroll offset when using mobile scrolling.
	var _mobileOffset = 0;

	//If the browser supports 3d transforms, this will be filled with 'translateZ(0)' (empty string otherwise).
	var _translateZ;

	//Will contain data about registered events by skrollr.
	var _registeredEvents = [];

	//Animation frame id returned by RequestAnimationFrame (or timeout when RAF is not supported).
	var _animFrame;

	//Expose skrollr as either a global variable or a require.js module.
	if(typeof define === 'function' && define.amd) {
		define([], function () {
			return skrollr;
		});
	} else if (typeof module !== 'undefined' && module.exports) {
		module.exports = skrollr;
	} else {
		window.skrollr = skrollr;
	}

}(window, document));