LAB.src.js

/*! LAB.js (LABjs :: Loading And Blocking JavaScript)
    v2.0 (c) Kyle Simpson
    MIT License
*/

(function(global){
	var _$LAB = global.$LAB,
	
		// constants for the valid keys of the options object
		_UseLocalXHR = "UseLocalXHR",
		_AlwaysPreserveOrder = "AlwaysPreserveOrder",
		_AllowDuplicates = "AllowDuplicates",
		_CacheBust = "CacheBust",
		/*!START_DEBUG*/_Debug = "Debug",/*!END_DEBUG*/
		_BasePath = "BasePath",
		
		// stateless variables used across all $LAB instances
		root_page = /^[^?#]*\//.exec(location.href)[0],
		root_domain = /^\w+\:\/\/\/?[^\/]+/.exec(root_page)[0],
		append_to = document.head || document.getElementsByTagName("head"),
		
		// inferences... ick, but still necessary
		opera_or_gecko = (global.opera && Object.prototype.toString.call(global.opera) == "[object Opera]") || ("MozAppearance" in document.documentElement.style),

/*!START_DEBUG*/
		// console.log() and console.error() wrappers
		log_msg = function(){}, 
		log_error = log_msg,
/*!END_DEBUG*/
		
		// feature sniffs (yay!)
		test_script_elem = document.createElement("script"),
		explicit_preloading = typeof test_script_elem.preload == "boolean", // http://wiki.whatwg.org/wiki/Script_Execution_Control#Proposal_1_.28Nicholas_Zakas.29
		real_preloading = explicit_preloading || (test_script_elem.readyState && test_script_elem.readyState == "uninitialized"), // will a script preload with `src` set before DOM append?
		script_ordered_async = !real_preloading && test_script_elem.async === true, // http://wiki.whatwg.org/wiki/Dynamic_Script_Execution_Order
		
		// XHR preloading (same-domain) and cache-preloading (remote-domain) are the fallbacks (for some browsers)
		xhr_or_cache_preloading = !real_preloading && !script_ordered_async && !opera_or_gecko
	;

/*!START_DEBUG*/
	// define console wrapper functions if applicable
	if (global.console && global.console.log) {
		if (!global.console.error) global.console.error = global.console.log;
		log_msg = function(msg) { global.console.log(msg); };
		log_error = function(msg,err) { global.console.error(msg,err); };
	}
/*!END_DEBUG*/

	// test for function
	function is_func(func) { return Object.prototype.toString.call(func) == "[object Function]"; }

	// test for array
	function is_array(arr) { return Object.prototype.toString.call(arr) == "[object Array]"; }

	// make script URL absolute/canonical
	function canonical_uri(src,base_path) {
		var absolute_regex = /^\w+\:\/\//;
		
		// is `src` is protocol-relative (begins with // or ///), prepend protocol
		if (/^\/\/\/?/.test(src)) {
			src = location.protocol + src;
		}
		// is `src` page-relative? (not an absolute URL, and not a domain-relative path, beginning with /)
		else if (!absolute_regex.test(src) && src[0] != "/") {
			// prepend `base_path`, if any
			src = (base_path || "") + src;
		}
		// make sure to return `src` as absolute
		return absolute_regex.test(src) ? src : ((src[0] == "/" ? root_domain : root_page) + src);
	}

	// merge `source` into `target`
	function merge_objs(source,target) {
		for (var k in source) { if (source.hasOwnProperty(k)) {
			target[k] = source[k]; // TODO: does this need to be recursive for our purposes?
		}}
		return target;
	}

	// does the chain group have any ready-to-execute scripts?
	function check_chain_group_scripts_ready(chain_group) {
		var any_scripts_ready = false;
		for (var i=0; i<chain_group.scripts.length; i++) {
			if (chain_group.scripts[i].ready && chain_group.scripts[i].exec_trigger) {
				any_scripts_ready = true;
				chain_group.scripts[i].exec_trigger();
				chain_group.scripts[i].exec_trigger = null;
			}
		}
		return any_scripts_ready;
	}

	// creates a script load listener
	function create_script_load_listener(elem,registry_item,flag,onload) {
		elem.onload = elem.onreadystatechange = function() {
			if ((elem.readyState && elem.readyState != "complete" && elem.readyState != "loaded") || registry_item[flag]) return;
			elem.onload = elem.onreadystatechange = null;
			onload();
		};
	}

	// script executed handler
	function script_executed(registry_item) {
		registry_item.ready = registry_item.finished = true;
		for (var i=0; i<registry_item.finished_listeners.length; i++) {
			setTimeout(registry_item.finished_listeners[i],0);
		}
		registry_item.ready_listeners = [];
		registry_item.finished_listeners = [];
	}

	// make the request for a scriptha
	function request_script(chain_opts,script_obj,registry_item,onload,preload_this_script) {
		// setTimeout() "yielding" prevents some weird race/crash conditions in older browsers
		setTimeout(function(){
			var script, src = script_obj.real_src, xhr;
			
			// don't proceed until `append_to` is ready to append to
			if ("item" in append_to) { // check if `append_to` ref is still a live node list
				if (!append_to[0]) { // `append_to` node not yet ready
					// try again in a little bit -- note: will re-call the anonymous function in the outer setTimeout, not the parent `request_script()`
					setTimeout(arguments.callee,25);
					return;
				}
				// reassign from live node list ref to pure node ref -- avoids nasty IE bug where changes to DOM invalidate live node lists
				append_to = append_to[0];
			}
			script = document.createElement("script");
			if (script_obj.type) script.type = script_obj.type;
			if (script_obj.charset) script.charset = script_obj.charset;
			
			// should preloading be used for this script?
			if (preload_this_script) {
				// real script preloading?
				if (real_preloading) {
					/*!START_DEBUG*/if (chain_opts[_Debug]) log_msg("start script preload: "+src);/*!END_DEBUG*/
					registry_item.elem = script;
					if (explicit_preloading) { // explicit preloading (aka, Zakas' proposal)
						script.preload = true;
						script.onpreload = onload;
					}
					else {
						script.onreadystatechange = function(){
							if (script.readyState == "loaded") onload();
							script.onreadystatechange = null;
						};
					}
					script.src = src;
					// NOTE: no append to DOM yet, appending will happen when ready to execute
				}
				// same-domain and XHR allowed? use XHR preloading
				else if (preload_this_script && src.indexOf(root_domain) == 0 && chain_opts[_UseLocalXHR]) {
					xhr = new XMLHttpRequest(); // note: IE never uses XHR (it supports true preloading), so no more need for ActiveXObject fallback for IE <= 7
					/*!START_DEBUG*/if (chain_opts[_Debug]) log_msg("start script preload (xhr): "+src);/*!END_DEBUG*/
					xhr.onreadystatechange = function() {
						if (xhr.readyState == 4) {
							xhr.onreadystatechange = function(){}; // fix a memory leak in IE
							registry_item.text = xhr.responseText + "\n//@ sourceURL=" + src; // http://blog.getfirebug.com/2009/08/11/give-your-eval-a-name-with-sourceurl/
							onload();
						}
					};
					xhr.open("GET",src);
					xhr.send();
				}
				// as a last resort, use cache-preloading
				else {
					/*!START_DEBUG*/if (chain_opts[_Debug]) log_msg("start script preload (cache): "+src);/*!END_DEBUG*/
					script.type = "text/cache-script";
					create_script_load_listener(script,registry_item,"ready",function() {
						append_to.removeChild(script);
						onload();
					});
					script.src = src;
					append_to.insertBefore(script,append_to.firstChild);
				}
			}
			// use async=false for ordered async? parallel-load-serial-execute http://wiki.whatwg.org/wiki/Dynamic_Script_Execution_Order
			else if (script_ordered_async) {
				/*!START_DEBUG*/if (chain_opts[_Debug]) log_msg("start script load (ordered async): "+src);/*!END_DEBUG*/
				script.async = false;
				create_script_load_listener(script,registry_item,"finished",onload);
				script.src = src;
				append_to.insertBefore(script,append_to.firstChild);
			}
			// otherwise, just a normal script element
			else {
				/*!START_DEBUG*/if (chain_opts[_Debug]) log_msg("start script load: "+src);/*!END_DEBUG*/
				create_script_load_listener(script,registry_item,"finished",onload);
				script.src = src;
				append_to.insertBefore(script,append_to.firstChild);
			}
		},0);
	}
		
	// create a clean instance of $LAB
	function create_sandbox() {
		var global_defaults = {},
			can_use_preloading = real_preloading || xhr_or_cache_preloading,
			queue = [],
			registry = {},
			instanceAPI
		;
		
		// global defaults
		global_defaults[_UseLocalXHR] = true;
		global_defaults[_AlwaysPreserveOrder] = false;
		global_defaults[_AllowDuplicates] = false;
		global_defaults[_CacheBust] = false;
		/*!START_DEBUG*/global_defaults[_Debug] = false;/*!END_DEBUG*/
		global_defaults[_BasePath] = "";

		// execute a script that has been preloaded already
		function execute_preloaded_script(chain_opts,script_obj,registry_item) {
			var script;
			
			function preload_execute_finished() {
				if (script != null) { // make sure this only ever fires once
					script_executed(registry_item);
					script = null;
				}
			}
			
			if (registry[script_obj.src].finished) return;
			if (!chain_opts[_AllowDuplicates]) registry[script_obj.src].finished = true;
			
			script = registry_item.elem || document.createElement("script");
			if (script_obj.type) script.type = script_obj.type;
			if (script_obj.charset) script.charset = script_obj.charset;
			create_script_load_listener(script,registry_item,"finished",preload_execute_finished);
			
			// script elem was real-preloaded
			if (registry_item.elem) {
				registry_item.elem = null;
			}
			// script was XHR preloaded
			else if (registry_item.text) {
				script.onload = script.onreadystatechange = null;	// script injection doesn't fire these events
				script.text = registry_item.text;
			}
			// script was cache-preloaded
			else {
				script.src = script_obj.real_src;
			}
			append_to.insertBefore(script,append_to.firstChild);

			// manually fire execution callback for injected scripts, since events don't fire
			if (registry_item.text) {
				preload_execute_finished();
			}
		}
	
		// process the script request setup
		function do_script(chain_opts,script_obj,chain_group,preload_this_script) {
			var registry_item,
				registry_items,
				ready_cb = function(){ script_obj.ready_cb(script_obj,function(){ execute_preloaded_script(chain_opts,script_obj,registry_item); }); },
				finished_cb = function(){ script_obj.finished_cb(script_obj,chain_group); }
			;
			
			script_obj.src = canonical_uri(script_obj.src,chain_opts[_BasePath]);
			script_obj.real_src = script_obj.src + 
				// append cache-bust param to URL?
				(chain_opts[_CacheBust] ? ((/\?.*$/.test(script_obj.src) ? "&_" : "?_") + ~~(Math.random()*1E9) + "=") : "")
			;
			
			if (!registry[script_obj.src]) registry[script_obj.src] = {items:[],finished:false};
			registry_items = registry[script_obj.src].items;

			// allowing duplicates, or is this the first recorded load of this script?
			if (chain_opts[_AllowDuplicates] || registry_items.length == 0) {
				registry_item = registry_items[registry_items.length] = {
					ready:false,
					finished:false,
					ready_listeners:[ready_cb],
					finished_listeners:[finished_cb]
				};

				request_script(chain_opts,script_obj,registry_item,
					// which callback type to pass?
					(
					 	(preload_this_script) ? // depends on script-preloading
						function(){
							registry_item.ready = true;
							for (var i=0; i<registry_item.ready_listeners.length; i++) {
								setTimeout(registry_item.ready_listeners[i],0);
							}
							registry_item.ready_listeners = [];
						} :
						function(){ script_executed(registry_item); }
					),
					// signal if script-preloading should be used or not
					preload_this_script
				);
			}
			else {
				registry_item = registry_items[0];
				if (registry_item.finished) {
					setTimeout(finished_cb,0);
				}
				else {
					registry_item.finished_listeners.push(finished_cb);
				}
			}
		}

		// creates a closure for each separate chain spawned from this $LAB instance, to keep state cleanly separated between chains
		function create_chain() {
			var chainedAPI,
				chain_opts = merge_objs(global_defaults,{}),
				chain = [],
				exec_cursor = 0,
				scripts_currently_loading = false,
				group
			;
			
			// called when a script has finished preloading
			function chain_script_ready(script_obj,exec_trigger) {
				/*!START_DEBUG*/if (chain_opts[_Debug]) log_msg("script preload finished: "+script_obj.real_src);/*!END_DEBUG*/
				script_obj.ready = true;
				script_obj.exec_trigger = exec_trigger;
				advance_exec_cursor(); // will only check for 'ready' scripts to be executed
			}

			// called when a script has finished executing
			function chain_script_executed(script_obj,chain_group) {
				/*!START_DEBUG*/if (chain_opts[_Debug]) log_msg("script execution finished: "+script_obj.real_src);/*!END_DEBUG*/
				script_obj.ready = script_obj.finished = true;
				script_obj.exec_trigger = null;
				// check if chain group is all finished
				for (var i=0; i<chain_group.scripts.length; i++) {
					if (!chain_group.scripts[i].finished) return;
				}
				// chain_group is all finished if we get this far
				chain_group.finished = true;
				advance_exec_cursor();
			}

			// main driver for executing each part of the chain
			function advance_exec_cursor() {
				while (exec_cursor < chain.length) {
					if (is_func(chain[exec_cursor])) {
						/*!START_DEBUG*/if (chain_opts[_Debug]) log_msg("$LAB.wait() executing: "+chain[exec_cursor]);/*!END_DEBUG*/
						try { chain[exec_cursor](); } catch (err) {
							/*!START_DEBUG*/if (chain_opts[_Debug]) log_error("$LAB.wait() error caught: ",err);/*!END_DEBUG*/
						}
					}
					else if (!chain[exec_cursor].finished) {
						if (check_chain_group_scripts_ready(chain[exec_cursor])) continue;
						break;
					}
					exec_cursor++;
				}
				// we've reached the end of the chain (so far)
				if (exec_cursor == chain.length) {
					scripts_currently_loading = false;
					group = false;
				}
			}
			
			// setup next chain script group
			function init_script_chain_group() {
				if (!group || !group.scripts) {
					chain.push(group = {scripts:[],finished:true});
				}
			}

			// API for $LAB chains
			chainedAPI = {
				// start loading one or more scripts
				script:function(){
					for (var i=0; i<arguments.length; i++) {
						(function(script_obj,script_list){
							var splice_args;
							
							if (!is_array(script_obj)) {
								script_list = [script_obj];
							}
							for (var j=0; j<script_list.length; j++) {
								init_script_chain_group();
								script_obj = script_list[j];
								
								if (is_func(script_obj)) script_obj = script_obj();
								if (!script_obj) continue;
								if (is_array(script_obj)) {
									splice_args = [].slice.call(script_obj);
									splice_args.push(j,1);
									script_list.splice.call(script_list,splice_args);
									j--;
									continue;
								}
								if (typeof script_obj == "string") script_obj = {src:script_obj};
								script_obj = merge_objs(script_obj,{
									ready:false,
									ready_cb:chain_script_ready,
									finished:false,
									finished_cb:chain_script_executed
								});
								group.finished = false;
								group.scripts.push(script_obj);
								
								do_script(chain_opts,script_obj,group,(can_use_preloading && scripts_currently_loading));
								scripts_currently_loading = true;
								
								if (chain_opts[_AlwaysPreserveOrder]) chainedAPI.wait();
							}
						})(arguments[i],arguments[i]);
					}
					return chainedAPI;
				},
				// force LABjs to pause in execution at this point in the chain, until the execution thus far finishes, before proceeding
				wait:function(){
					if (arguments.length > 0) {
						for (var i=0; i<arguments.length; i++) {
							chain.push(arguments[i]);
						}
						group = chain[chain.length-1];
					}
					else group = false;
					
					advance_exec_cursor();
					
					return chainedAPI;
				}
			};

			// the first chain link API (includes `setOptions` only this first time)
			return {
				script:chainedAPI.script, 
				wait:chainedAPI.wait, 
				setOptions:function(opts){
					merge_objs(opts,chain_opts);
					return chainedAPI;
				}
			};
		}

		// API for each initial $LAB instance (before chaining starts)
		instanceAPI = {
			// main API functions
			setGlobalDefaults:function(opts){
				merge_objs(opts,global_defaults);
				return instanceAPI;
			},
			setOptions:function(){
				return create_chain().setOptions.apply(null,arguments);
			},
			script:function(){
				return create_chain().script.apply(null,arguments);
			},
			wait:function(){
				return create_chain().wait.apply(null,arguments);
			},

			// built-in queuing for $LAB `script()` and `wait()` calls
			// useful for building up a chain programmatically across various script locations, and simulating
			// execution of the chain
			queueScript:function(){
				queue[queue.length] = {type:"script", args:[].slice.call(arguments)};
				return instanceAPI;
			},
			queueWait:function(){
				queue[queue.length] = {type:"wait", args:[].slice.call(arguments)};
				return instanceAPI;
			},
			runQueue:function(){
				var $L = instanceAPI, len=queue.length, i=len, val;
				for (;--i>=0;) {
					val = queue.shift();
					$L = $L[val.type].apply(null,val.args);
				}
				return $L;
			},

			// rollback `[global].$LAB` to what it was before this file was loaded, the return this current instance of $LAB
			noConflict:function(){
				global.$LAB = _$LAB;
				return instanceAPI;
			},

			// create another clean instance of $LAB
			sandbox:function(){
				return create_sandbox();
			}
		};

		return instanceAPI;
	}

	// create the main instance of $LAB
	global.$LAB = create_sandbox();


	/* The following "hack" was suggested by Andrea Giammarchi and adapted from: http://webreflection.blogspot.com/2009/11/195-chars-to-help-lazy-loading.html
	   NOTE: this hack only operates in FF and then only in versions where document.readyState is not present (FF < 3.6?).
	   
	   The hack essentially "patches" the **page** that LABjs is loaded onto so that it has a proper conforming document.readyState, so that if a script which does 
	   proper and safe dom-ready detection is loaded onto a page, after dom-ready has passed, it will still be able to detect this state, by inspecting the now hacked 
	   document.readyState property. The loaded script in question can then immediately trigger any queued code executions that were waiting for the DOM to be ready. 
	   For instance, jQuery 1.4+ has been patched to take advantage of document.readyState, which is enabled by this hack. But 1.3.2 and before are **not** safe or 
	   fixed by this hack, and should therefore **not** be lazy-loaded by script loader tools such as LABjs.
	*/ 
	(function(addEvent,domLoaded,handler){
		if (document.readyState == null && document[addEvent]){
			document.readyState = "loading";
			document[addEvent](domLoaded,handler = function(){
				document.removeEventListener(domLoaded,handler,false);
				document.readyState = "complete";
			},false);
		}
	})("addEventListener","DOMContentLoaded");

})(this);