holder.js

/*

Holder - 1.4 - client side image placeholders
(c) 2012 Ivan Malopinsky / http://imsky.co

Provided under the Apache 2.0 License: http://www.apache.org/licenses/LICENSE-2.0
Commercial use requires attribution.

*/

var Holder = Holder || {};
(function (app, win) {

var preempted = false,
fallback = false,
canvas = document.createElement('canvas');

//getElementsByClassName polyfill
document.getElementsByClassName||(document.getElementsByClassName=function(e){var t=document,n,r,i,s=[];if(t.querySelectorAll)return t.querySelectorAll("."+e);if(t.evaluate){r=".//*[contains(concat(' ', @class, ' '), ' "+e+" ')]",n=t.evaluate(r,t,null,0,null);while(i=n.iterateNext())s.push(i)}else{n=t.getElementsByTagName("*"),r=new RegExp("(^|\\s)"+e+"(\\s|$)");for(i=0;i<n.length;i++)r.test(n[i].className)&&s.push(n[i])}return s})

//getComputedStyle polyfill
window.getComputedStyle||(window.getComputedStyle=function(e,t){return this.el=e,this.getPropertyValue=function(t){var n=/(\-([a-z]){1})/g;return t=="float"&&(t="styleFloat"),n.test(t)&&(t=t.replace(n,function(){return arguments[2].toUpperCase()})),e.currentStyle[t]?e.currentStyle[t]:null},this})

//http://javascript.nwbox.com/ContentLoaded by Diego Perini with modifications
function contentLoaded(n,t){var l="complete",s="readystatechange",u=!1,h=u,c=!0,i=n.document,a=i.documentElement,e=i.addEventListener?"addEventListener":"attachEvent",v=i.addEventListener?"removeEventListener":"detachEvent",f=i.addEventListener?"":"on",r=function(e){(e.type!=s||i.readyState==l)&&((e.type=="load"?n:i)[v](f+e.type,r,u),!h&&(h=!0)&&t.call(n,null))},o=function(){try{a.doScroll("left")}catch(n){setTimeout(o,50);return}r("poll")};if(i.readyState==l)t.call(n,"lazy");else{if(i.createEventObject&&a.doScroll){try{c=!n.frameElement}catch(y){}c&&o()}i[e](f+"DOMContentLoaded",r,u),i[e](f+s,r,u),n[e](f+"load",r,u)}};

//https://gist.github.com/991057 by Jed Schmidt with modifications
function selector(a){
	a=a.match(/^(\W)?(.*)/);var b=document["getElement"+(a[1]?a[1]=="#"?"ById":"sByClassName":"sByTagName")](a[2]);
	var ret=[];	b!=null&&(b.length?ret=b:b.length==0?ret=b:ret=[b]);	return ret;
}

//shallow object property extend
function extend(a,b){var c={};for(var d in a)c[d]=a[d];for(var e in b)c[e]=b[e];return c}

function draw(ctx, dimensions, template) {
	var dimension_arr = [dimensions.height, dimensions.width].sort();
	var maxFactor = Math.round(dimension_arr[1] / 16),
		minFactor = Math.round(dimension_arr[0] / 16);
	var text_height = Math.max(template.size, maxFactor);
	canvas.width = dimensions.width;
	canvas.height = dimensions.height;
	ctx.textAlign = "center";
	ctx.textBaseline = "middle";
	ctx.fillStyle = template.background;
	ctx.fillRect(0, 0, dimensions.width, dimensions.height);
	ctx.fillStyle = template.foreground;
	ctx.font = "bold " + text_height + "px sans-serif";
	var text = template.text ? template.text : (dimensions.width + "x" + dimensions.height);
	if (Math.round(ctx.measureText(text).width) / dimensions.width > 1) {
		text_height = Math.max(minFactor, template.size);
	}
	ctx.font = "bold " + text_height + "px sans-serif";
	ctx.fillText(text, (dimensions.width / 2), (dimensions.height / 2), dimensions.width);
	return canvas.toDataURL("image/png");
}

if (!canvas.getContext) {
	fallback = true;
} else {
	if (canvas.toDataURL("image/png").indexOf("data:image/png") < 0) {
		//Android doesn't support data URI
		fallback = true;
	} else {
		var ctx = canvas.getContext("2d");
	}
}

function render(mode, el, holder, src){

	var dimensions = holder.dimensions, theme = holder.theme, text = holder.text;
	var dimensions_caption = dimensions.width + "x" + dimensions.height;
		theme = (text ? extend(theme, {	text: text	}) : theme);
	
	if(mode == "image"){
		el.setAttribute("data-src", src);
		el.setAttribute("alt", text ? text : theme.text ? theme.text + " [" + dimensions_caption + "]" : dimensions_caption);
		el.style.width = dimensions.width + "px";
		el.style.height = dimensions.height + "px";
		el.style.backgroundColor = theme.background;
		
		if(!fallback){
			el.setAttribute("src", draw(ctx, dimensions, theme));
		}
	}
	else {
		if(!fallback){
			el.style.backgroundImage = "url("+draw(ctx, dimensions, theme)+")";
		}
	}
	
};

function parse_flags(flags, options){
	
	var ret = {
		theme: settings.themes.gray
		}, render = false;
	
	for (sl = flags.length, j = 0; j < sl; j++) {
				if (app.flags.dimensions.match(flags[j])) {
					render = true;
					ret.dimensions = app.flags.dimensions.output(flags[j]);
				} else if (app.flags.colors.match(flags[j])) {
					ret.theme = app.flags.colors.output(flags[j]);
				} else if (options.themes[flags[j]]) {
					//If a theme is specified, it will override custom colors
					ret.theme = options.themes[flags[j]];
				} else if (app.flags.text.match(flags[j])) {
					ret.text = app.flags.text.output(flags[j]);
				}
	}
	
	return render ? ret : false;
	
};

var settings = {
	domain: "holder.js",
	images: "img",
	elements: ".holderjs",
	themes: {
		"gray": {
			background: "#eee",
			foreground: "#aaa",
			size: 12
		},
		"social": {
			background: "#3a5a97",
			foreground: "#fff",
			size: 12
		},
		"industrial": {
			background: "#434A52",
			foreground: "#C2F200",
			size: 12
		}
	}
};


app.flags = {
	dimensions: {
		regex: /([0-9]+)x([0-9]+)/,
		output: function(val){
			var exec = this.regex.exec(val);
			return {
				width: +exec[1],
				height: +exec[2]
			}
		}
	},
	colors: {
		regex: /#([0-9a-f]{3,})\:#([0-9a-f]{3,})/i,
		output: function(val){
			var exec = this.regex.exec(val);
			return {
					size: settings.themes.gray.size,
					foreground: "#" + exec[2],
					background: "#" + exec[1]
					}
		}
	},
	text: {
		regex: /text\:(.*)/,
		output: function(val){
			return this.regex.exec(val)[1];
		}
	}
}

for(var flag in app.flags){
	app.flags[flag].match = function (val){
		return val.match(this.regex)
	}
}

app.add_theme = function (name, theme) {
	name != null && theme != null && (settings.themes[name] = theme);
	return app;
};

app.add_image = function (src, el) {
	var node = selector(el);
	if (node.length) {
		for (var i = 0, l = node.length; i < l; i++) {
			var img = document.createElement("img")
			img.setAttribute("data-src", src);
			node[i].appendChild(img);
		}
	}
	return app;
};

app.run = function (o) {
	var options = extend(settings, o),
		images = selector(options.images),
		elements = selector(options.elements),
		preempted = true;

	var cssregex = new RegExp(options.domain+"\/(.*?)\"?\\)");
	
	for(var l = elements.length, i = 0; i < l; i++){
		var src = window.getComputedStyle(elements[i],null).getPropertyValue("background-image");
		var flags = src.match(cssregex);
		if(flags){
			var holder = parse_flags(flags[1].split("/"), options);
			if(holder){
				render("background", elements[i], holder, src);
			}
		}
	}

	for (var l = images.length, i = 0; i < l; i++) {
		var src = images[i].getAttribute("data-src") || images[i].getAttribute("src");
		if (src.indexOf(options.domain)>=0) {
			var holder = parse_flags(src.substr(src.lastIndexOf(options.domain) + options.domain.length + 1).split("/"), options);
			if (holder) {
				render("image", images[i], holder, src);
			}
		}
	}
	return app;
};

contentLoaded(win, function () {
	preempted || app.run()
});

})(Holder, window);