HayMaker/jquery.haymaker.js at master · bbarr/HayMaker · GitHub

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/**
 *  A preloader of images/ajax requests.
 *  Uses sessionStorage to try and not "cache" the same image twice.
 *  Releases UI thread every 300ms.
 *
 *  Example:
 *    var hm = new $.HayMaker();
 *    hm.queue(['an_image.jpg', '/some/service', 'another_image.png']);
 *
 *  @author Brendan Barr - brendanbarr.web@gmail.com
 */

(function($) {

	if (typeof $.HayMaker !== 'undefined') {
		throw new Error('What are the chances of another plugin called HayMaker?! Or, is this script being loaded multiple times?...');
	}

	$.HayMaker = function() {

		if (!(this instanceof $.HayMaker)) {
			return new $.HayMaker();
		}

		$.HayMaker.count++;
		this.cache = {};
		this.queue = [];
		this.working = false;
		this.session = (window.sessionStorage) ? window.sessionStorage.hay = '' : '';
		this.start_time;

		// image for capturing preloaded images
		var _this = this;
		this.img = $('<img />')
			.attr({ 'id': 'hay_maker_image_' + $.HayMaker.count, 'style' : 'display: none' })
			.load(function() { _this._process(this.src); })
			.appendTo(document.body)[0];

	};

	$.HayMaker.count = 0;

	$.HayMaker.prototype = {

		queue: function(uris) {

			if (typeof uris === 'string') {
				this.queue.push(uris);
			}
			else {
				this.queue = this.queues.concat(uris);
			}

			var _this = this;
			$(document)[ ($.HayMaker.waiting) ? 'ajaxStop' : 'ready' ](function() {
				$.HayMaker.waiting = false;
				_this.start();
			});
		},

		pause: function() {
			this.waiting = true;
		},

		start: function() {
			this.start_time = $.now();
			this._dequeue();
		},

		_dequeue: function() {

			this.working = (!this.waiting && this.queue.length > 0);
			if (!this.working) {
				return;
			}

			var uri = this.queue.shift();
			if (this._is_logged(uri)) {
				this_dequeue();
			}

			if (/(.jpg|.png|.gif)$/.test(uri)) {
				this.img.src = uri;
			}
			else {
				var _this = this;
				$.get(uri, function(data) {
					_this._process(uri, data);
				});
			}
		},

		_process: function(uri, data) {

			if (data) {
				this.cache[uri] = data;
			}

			// if has been loading for more than 300ms, release ui thread
			if (this.start_time - $.now() > 300) {
				var _this = this;
				window.setTimeout(_this.start, 0);
			}
			else {
				this._dequeue();
			}
		},

		_log: function(uri) {
			this.session += (uri + ';');
		}

		_is_logged: function(uri) {
			return (this.session.indexOf(uri) > -1);
		}

	};

	// detect start of any initial ajax requests
	$(window).ajaxStart(function() {
		$.HayMaker.waiting = true;
	});

})(jQuery);