lazysizes.js

(function(window, factory) {
	var lazySizes = factory(window, window.document);
	window.lazySizes = lazySizes;
	if(typeof module == 'object' && module.exports){
		module.exports = lazySizes;
	}
}(window, function l(window, document) {
	'use strict';
	/*jshint eqnull:true */
	if(!document.getElementsByClassName){return;}

	var lazysizes, lazySizesConfig;

	var docElem = document.documentElement;

	var Date = window.Date;

	var supportPicture = window.HTMLPictureElement;

	var _addEventListener = 'addEventListener';

	var _getAttribute = 'getAttribute';

	var addEventListener = window[_addEventListener];

	var setTimeout = window.setTimeout;

	var requestAnimationFrame = window.requestAnimationFrame || setTimeout;

	var requestIdleCallback = window.requestIdleCallback;

	var regPicture = /^picture$/i;

	var loadEvents = ['load', 'error', 'lazyincluded', '_lazyloaded'];

	var regClassCache = {};

	var forEach = Array.prototype.forEach;

	var hasClass = function(ele, cls) {
		if(!regClassCache[cls]){
			regClassCache[cls] = new RegExp('(\\s|^)'+cls+'(\\s|$)');
		}
		return regClassCache[cls].test(ele[_getAttribute]('class') || '') && regClassCache[cls];
	};

	var addClass = function(ele, cls) {
		if (!hasClass(ele, cls)){
			ele.setAttribute('class', (ele[_getAttribute]('class') || '').trim() + ' ' + cls);
		}
	};

	var removeClass = function(ele, cls) {
		var reg;
		if ((reg = hasClass(ele,cls))) {
			ele.setAttribute('class', (ele[_getAttribute]('class') || '').replace(reg, ' '));
		}
	};

	var addRemoveLoadEvents = function(dom, fn, add){
		var action = add ? _addEventListener : 'removeEventListener';
		if(add){
			addRemoveLoadEvents(dom, fn);
		}
		loadEvents.forEach(function(evt){
			dom[action](evt, fn);
		});
	};

	var triggerEvent = function(elem, name, detail, noBubbles, noCancelable){
		var event = document.createEvent('CustomEvent');

		if(!detail){
			detail = {};
		}

		detail.instance = lazysizes;

		event.initCustomEvent(name, !noBubbles, !noCancelable, detail);

		elem.dispatchEvent(event);
		return event;
	};

	var updatePolyfill = function (el, full){
		var polyfill;
		if( !supportPicture && ( polyfill = (window.picturefill || lazySizesConfig.pf) ) ){
			polyfill({reevaluate: true, elements: [el]});
		} else if(full && full.src){
			el.src = full.src;
		}
	};

	var getCSS = function (elem, style){
		return (getComputedStyle(elem, null) || {})[style];
	};

	var getWidth = function(elem, parent, width){
		width = width || elem.offsetWidth;

		while(width < lazySizesConfig.minSize && parent && !elem._lazysizesWidth){
			width =  parent.offsetWidth;
			parent = parent.parentNode;
		}

		return width;
	};

	var rAF = (function(){
		var running, waiting;
		var firstFns = [];
		var secondFns = [];
		var fns = firstFns;

		var run = function(){
			var runFns = fns;

			fns = firstFns.length ? secondFns : firstFns;

			running = true;
			waiting = false;

			while(runFns.length){
				runFns.shift()();
			}

			running = false;
		};

		var rafBatch = function(fn, queue){
			if(running && !queue){
				fn.apply(this, arguments);
			} else {
				fns.push(fn);

				if(!waiting){
					waiting = true;
					(document.hidden ? setTimeout : requestAnimationFrame)(run);
				}
			}
		};

		rafBatch._lsFlush = run;

		return rafBatch;
	})();

	var rAFIt = function(fn, simple){
		return simple ?
			function() {
				rAF(fn);
			} :
			function(){
				var that = this;
				var args = arguments;
				rAF(function(){
					fn.apply(that, args);
				});
			}
		;
	};

	var throttle = function(fn){
		var running;
		var lastTime = 0;
		var gDelay = 125;
		var RIC_DEFAULT_TIMEOUT = 666;
		var rICTimeout = RIC_DEFAULT_TIMEOUT;
		var run = function(){
			running = false;
			lastTime = Date.now();
			fn();
		};
		var idleCallback = requestIdleCallback ?
			function(){
				requestIdleCallback(run, {timeout: rICTimeout});
				if(rICTimeout !== RIC_DEFAULT_TIMEOUT){
					rICTimeout = RIC_DEFAULT_TIMEOUT;
				}
			}:
			rAFIt(function(){
				setTimeout(run);
			}, true)
		;

		return function(isPriority){
			var delay;
			if((isPriority = isPriority === true)){
				rICTimeout = 44;
			}

			if(running){
				return;
			}

			running =  true;

			delay = gDelay - (Date.now() - lastTime);

			if(delay < 0){
				delay = 0;
			}

			if(isPriority || (delay < 9 && requestIdleCallback)){
				idleCallback();
			} else {
				setTimeout(idleCallback, delay);
			}
		};
	};

	//based on http://modernjavascript.blogspot.de/2013/08/building-better-debounce.html
	var debounce = function(func) {
		var timeout, timestamp;
		var wait = 99;
		var run = function(){
			timeout = null;
			func();
		};
		var later = function() {
			var last = Date.now() - timestamp;

			if (last < wait) {
				setTimeout(later, wait - last);
			} else {
				(requestIdleCallback || run)(run);
			}
		};

		return function() {
			timestamp = Date.now();

			if (!timeout) {
				timeout = setTimeout(later, wait);
			}
		};
	};


	var loader = (function(){
		var preloadElems, isCompleted, resetPreloadingTimer, loadMode, started;

		var eLvW, elvH, eLtop, eLleft, eLright, eLbottom;

		var defaultExpand, preloadExpand, hFac;

		var regImg = /^img$/i;
		var regIframe = /^iframe$/i;

		var supportScroll = ('onscroll' in window) && !(/glebot/.test(navigator.userAgent));

		var shrinkExpand = 0;
		var currentExpand = 0;

		var isLoading = 0;
		var lowRuns = -1;

		var resetPreloading = function(e){
			isLoading--;
			if(e && e.target){
				addRemoveLoadEvents(e.target, resetPreloading);
			}

			if(!e || isLoading < 0 || !e.target){
				isLoading = 0;
			}
		};

		var isNestedVisible = function(elem, elemExpand){
			var outerRect;
			var parent = elem;
			var visible = getCSS(document.body, 'visibility') == 'hidden' || getCSS(elem, 'visibility') != 'hidden';

			eLtop -= elemExpand;
			eLbottom += elemExpand;
			eLleft -= elemExpand;
			eLright += elemExpand;

			while(visible && (parent = parent.offsetParent) && parent != document.body && parent != docElem){
				visible = ((getCSS(parent, 'opacity') || 1) > 0);

				if(visible && getCSS(parent, 'overflow') != 'visible'){
					outerRect = parent.getBoundingClientRect();
					visible = eLright > outerRect.left &&
						eLleft < outerRect.right &&
						eLbottom > outerRect.top - 1 &&
						eLtop < outerRect.bottom + 1
					;
				}
			}

			return visible;
		};

		var checkElements = function() {
			var eLlen, i, rect, autoLoadElem, loadedSomething, elemExpand, elemNegativeExpand, elemExpandVal, beforeExpandVal;

			var lazyloadElems = lazysizes.elements;

			if((loadMode = lazySizesConfig.loadMode) && isLoading < 8 && (eLlen = lazyloadElems.length)){

				i = 0;

				lowRuns++;

				if(preloadExpand == null){
					if(!('expand' in lazySizesConfig)){
						lazySizesConfig.expand = docElem.clientHeight > 500 && docElem.clientWidth > 500 ? 500 : 370;
					}

					defaultExpand = lazySizesConfig.expand;
					preloadExpand = defaultExpand * lazySizesConfig.expFactor;
				}

				if(currentExpand < preloadExpand && isLoading < 1 && lowRuns > 2 && loadMode > 2 && !document.hidden){
					currentExpand = preloadExpand;
					lowRuns = 0;
				} else if(loadMode > 1 && lowRuns > 1 && isLoading < 6){
					currentExpand = defaultExpand;
				} else {
					currentExpand = shrinkExpand;
				}

				for(; i < eLlen; i++){

					if(!lazyloadElems[i] || lazyloadElems[i]._lazyRace){continue;}

					if(!supportScroll){unveilElement(lazyloadElems[i]);continue;}

					if(!(elemExpandVal = lazyloadElems[i][_getAttribute]('data-expand')) || !(elemExpand = elemExpandVal * 1)){
						elemExpand = currentExpand;
					}

					if(beforeExpandVal !== elemExpand){
						eLvW = innerWidth + (elemExpand * hFac);
						elvH = innerHeight + elemExpand;
						elemNegativeExpand = elemExpand * -1;
						beforeExpandVal = elemExpand;
					}

					rect = lazyloadElems[i].getBoundingClientRect();

					if ((eLbottom = rect.bottom) >= elemNegativeExpand &&
						(eLtop = rect.top) <= elvH &&
						(eLright = rect.right) >= elemNegativeExpand * hFac &&
						(eLleft = rect.left) <= eLvW &&
						(eLbottom || eLright || eLleft || eLtop) &&
						(lazySizesConfig.loadHidden || getCSS(lazyloadElems[i], 'visibility') != 'hidden') &&
						((isCompleted && isLoading < 3 && !elemExpandVal && (loadMode < 3 || lowRuns < 4)) || isNestedVisible(lazyloadElems[i], elemExpand))){
						unveilElement(lazyloadElems[i]);
						loadedSomething = true;
						if(isLoading > 9){break;}
					} else if(!loadedSomething && isCompleted && !autoLoadElem &&
						isLoading < 4 && lowRuns < 4 && loadMode > 2 &&
						(preloadElems[0] || lazySizesConfig.preloadAfterLoad) &&
						(preloadElems[0] || (!elemExpandVal && ((eLbottom || eLright || eLleft || eLtop) || lazyloadElems[i][_getAttribute](lazySizesConfig.sizesAttr) != 'auto')))){
						autoLoadElem = preloadElems[0] || lazyloadElems[i];
					}
				}

				if(autoLoadElem && !loadedSomething){
					unveilElement(autoLoadElem);
				}
			}
		};

		var throttledCheckElements = throttle(checkElements);

		var switchLoadingClass = function(e){
			addClass(e.target, lazySizesConfig.loadedClass);
			removeClass(e.target, lazySizesConfig.loadingClass);
			addRemoveLoadEvents(e.target, rafSwitchLoadingClass);
			triggerEvent(e.target, 'lazyloaded');
		};
		var rafedSwitchLoadingClass = rAFIt(switchLoadingClass);
		var rafSwitchLoadingClass = function(e){
			rafedSwitchLoadingClass({target: e.target});
		};

		var changeIframeSrc = function(elem, src){
			try {
				elem.contentWindow.location.replace(src);
			} catch(e){
				elem.src = src;
			}
		};

		var handleSources = function(source){
			var customMedia;

			var sourceSrcset = source[_getAttribute](lazySizesConfig.srcsetAttr);

			if( (customMedia = lazySizesConfig.customMedia[source[_getAttribute]('data-media') || source[_getAttribute]('media')]) ){
				source.setAttribute('media', customMedia);
			}

			if(sourceSrcset){
				source.setAttribute('srcset', sourceSrcset);
			}
		};

		var lazyUnveil = rAFIt(function (elem, detail, isAuto, sizes, isImg){
			var src, srcset, parent, isPicture, event, firesLoad;

			if(!(event = triggerEvent(elem, 'lazybeforeunveil', detail)).defaultPrevented){

				if(sizes){
					if(isAuto){
						addClass(elem, lazySizesConfig.autosizesClass);
					} else {
						elem.setAttribute('sizes', sizes);
					}
				}

				srcset = elem[_getAttribute](lazySizesConfig.srcsetAttr);
				src = elem[_getAttribute](lazySizesConfig.srcAttr);

				if(isImg) {
					parent = elem.parentNode;
					isPicture = parent && regPicture.test(parent.nodeName || '');
				}

				firesLoad = detail.firesLoad || (('src' in elem) && (srcset || src || isPicture));

				event = {target: elem};

				if(firesLoad){
					addRemoveLoadEvents(elem, resetPreloading, true);
					clearTimeout(resetPreloadingTimer);
					resetPreloadingTimer = setTimeout(resetPreloading, 2500);

					addClass(elem, lazySizesConfig.loadingClass);
					addRemoveLoadEvents(elem, rafSwitchLoadingClass, true);
				}

				if(isPicture){
					forEach.call(parent.getElementsByTagName('source'), handleSources);
				}

				if(srcset){
					elem.setAttribute('srcset', srcset);
				} else if(src && !isPicture){
					if(regIframe.test(elem.nodeName)){
						changeIframeSrc(elem, src);
					} else {
						elem.src = src;
					}
				}

				if(isImg && (srcset || isPicture)){
					updatePolyfill(elem, {src: src});
				}
			}

			if(elem._lazyRace){
				delete elem._lazyRace;
			}
			removeClass(elem, lazySizesConfig.lazyClass);

			rAF(function(){
				if( !firesLoad || (elem.complete && elem.naturalWidth > 1)){
					if(firesLoad){
						resetPreloading(event);
					} else {
						isLoading--;
					}
					switchLoadingClass(event);
				}
			}, true);
		});

		var unveilElement = function (elem){
			var detail;

			var isImg = regImg.test(elem.nodeName);

			//allow using sizes="auto", but don't use. it's invalid. Use data-sizes="auto" or a valid value for sizes instead (i.e.: sizes="80vw")
			var sizes = isImg && (elem[_getAttribute](lazySizesConfig.sizesAttr) || elem[_getAttribute]('sizes'));
			var isAuto = sizes == 'auto';

			if( (isAuto || !isCompleted) && isImg && (elem[_getAttribute]('src') || elem.srcset) && !elem.complete && !hasClass(elem, lazySizesConfig.errorClass)){return;}

			detail = triggerEvent(elem, 'lazyunveilread').detail;

			if(isAuto){
				 autoSizer.updateElem(elem, true, elem.offsetWidth);
			}

			elem._lazyRace = true;
			isLoading++;

			lazyUnveil(elem, detail, isAuto, sizes, isImg);
		};

		var onload = function(){
			if(isCompleted){return;}
			if(Date.now() - started < 999){
				setTimeout(onload, 999);
				return;
			}
			var afterScroll = debounce(function(){
				lazySizesConfig.loadMode = 3;
				throttledCheckElements();
			});

			isCompleted = true;

			lazySizesConfig.loadMode = 3;

			throttledCheckElements();

			addEventListener('scroll', function(){
				if(lazySizesConfig.loadMode == 3){
					lazySizesConfig.loadMode = 2;
				}
				afterScroll();
			}, true);
		};

		return {
			_: function(){
				started = Date.now();

				lazysizes.elements = document.getElementsByClassName(lazySizesConfig.lazyClass);
				preloadElems = document.getElementsByClassName(lazySizesConfig.lazyClass + ' ' + lazySizesConfig.preloadClass);
				hFac = lazySizesConfig.hFac;

				addEventListener('scroll', throttledCheckElements, true);

				addEventListener('resize', throttledCheckElements, true);

				if(window.MutationObserver){
					new MutationObserver( throttledCheckElements ).observe( docElem, {childList: true, subtree: true, attributes: true} );
				} else {
					docElem[_addEventListener]('DOMNodeInserted', throttledCheckElements, true);
					docElem[_addEventListener]('DOMAttrModified', throttledCheckElements, true);
					setInterval(throttledCheckElements, 999);
				}

				addEventListener('hashchange', throttledCheckElements, true);

				//, 'fullscreenchange'
				['focus', 'mouseover', 'click', 'load', 'transitionend', 'animationend', 'webkitAnimationEnd'].forEach(function(name){
					document[_addEventListener](name, throttledCheckElements, true);
				});

				if((/d$|^c/.test(document.readyState))){
					onload();
				} else {
					addEventListener('load', onload);
					document[_addEventListener]('DOMContentLoaded', throttledCheckElements);
					setTimeout(onload, 20000);
				}

				if(lazysizes.elements.length){
					checkElements();
					rAF._lsFlush();
				} else {
					throttledCheckElements();
				}
			},
			checkElems: throttledCheckElements,
			unveil: unveilElement
		};
	})();


	var autoSizer = (function(){
		var autosizesElems;

		var sizeElement = rAFIt(function(elem, parent, event, width){
			var sources, i, len;
			elem._lazysizesWidth = width;
			width += 'px';

			elem.setAttribute('sizes', width);

			if(regPicture.test(parent.nodeName || '')){
				sources = parent.getElementsByTagName('source');
				for(i = 0, len = sources.length; i < len; i++){
					sources[i].setAttribute('sizes', width);
				}
			}

			if(!event.detail.dataAttr){
				updatePolyfill(elem, event.detail);
			}
		});
		var getSizeElement = function (elem, dataAttr, width){
			var event;
			var parent = elem.parentNode;

			if(parent){
				width = getWidth(elem, parent, width);
				event = triggerEvent(elem, 'lazybeforesizes', {width: width, dataAttr: !!dataAttr});

				if(!event.defaultPrevented){
					width = event.detail.width;

					if(width && width !== elem._lazysizesWidth){
						sizeElement(elem, parent, event, width);
					}
				}
			}
		};

		var updateElementsSizes = function(){
			var i;
			var len = autosizesElems.length;
			if(len){
				i = 0;

				for(; i < len; i++){
					getSizeElement(autosizesElems[i]);
				}
			}
		};

		var debouncedUpdateElementsSizes = debounce(updateElementsSizes);

		return {
			_: function(){
				autosizesElems = document.getElementsByClassName(lazySizesConfig.autosizesClass);
				addEventListener('resize', debouncedUpdateElementsSizes);
			},
			checkElems: debouncedUpdateElementsSizes,
			updateElem: getSizeElement
		};
	})();

	var init = function(){
		if(!init.i){
			init.i = true;
			autoSizer._();
			loader._();
		}
	};

	(function(){
		var prop;

		var lazySizesDefaults = {
			lazyClass: 'lazyload',
			loadedClass: 'lazyloaded',
			loadingClass: 'lazyloading',
			preloadClass: 'lazypreload',
			errorClass: 'lazyerror',
			//strictClass: 'lazystrict',
			autosizesClass: 'lazyautosizes',
			srcAttr: 'data-src',
			srcsetAttr: 'data-srcset',
			sizesAttr: 'data-sizes',
			//preloadAfterLoad: false,
			minSize: 40,
			customMedia: {},
			init: true,
			expFactor: 1.5,
			hFac: 0.8,
			loadMode: 2,
			loadHidden: true,
		};

		lazySizesConfig = window.lazySizesConfig || window.lazysizesConfig || {};

		for(prop in lazySizesDefaults){
			if(!(prop in lazySizesConfig)){
				lazySizesConfig[prop] = lazySizesDefaults[prop];
			}
		}

		window.lazySizesConfig = lazySizesConfig;

		setTimeout(function(){
			if(lazySizesConfig.init){
				init();
			}
		});
	})();

	lazysizes = {
		cfg: lazySizesConfig,
		autoSizer: autoSizer,
		loader: loader,
		init: init,
		uP: updatePolyfill,
		aC: addClass,
		rC: removeClass,
		hC: hasClass,
		fire: triggerEvent,
		gW: getWidth,
		rAF: rAF,
	};

	return lazysizes;
}
));