scriptLoader.js

/*	----- ScriptLoader -----
	Randy Hoggard 2016
	A constructor to create an object that can dynamically add script to document
	------------------------ */
function ScriptLoader(config,callback){//doneCallback,errorCallback){
	//***** Private Members ****************************************************
	var 	scripts,
			parent,
			done,
			oldOnload,
			mode;
	
	//***** Public Members *****************************************************
	this.loadFile = loadFile;
	this.loadText = loadText;
	
	//***** Initialize *********************************************************
	//attach init to document as soon as DOM is ready
	attachInit();
	
	//***** Private Methods ****************************************************
	function init(){
		scripts = [];
		done = [];	
		if(config){
			//config present
			//use config to set member values
			if(config.scripts){
				if(isArray(config.scripts)){
					scripts = config.scripts;
				} else {
					callback(new Error("Invalid config value 'scripts'. 'scripts' must be an array of strings (urls)."),"error" );
					//need to throw Error here!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
				}
				
			} else {
				//use default
				scripts = [];
			}
			if(config.appendTo){
				switch(config.appendTo){
					case "head":
					//append to head
						parent = document.getElementsByTagName('head')[0];
						break;
					case "body":
					//append to body
						parent = document.getElementsByTagName('body')[0];
						break;
					case "default":
					//use default,attatch to parent of first script
						parent = document.getElementsByTagName('script')[0].parentNode;	
						break;
					default:
					//invalid value, throw error
					callback(new Error("invalid config value 'appendTo'. 'appendTo' must be a string that matches one of the following values: 'head','body','default'."),"error");	
				}
			} else {
				//use default,attatch to parent of first script
				parent = document.getElementsByTagName('script')[0].parentNode;	
			}
			if(config.mode){
				if(config.mode === "async" || config.mode === "sync" || config.mode === "fastSync"){
					//valid mode, set mode
					mode = config.mode;
				} else {
					//invalid mode, throw error
					callback(new Error("Invalid config value 'mode'. 'mode' must be a string that matches one of the following values: 'async','fastSync','sync'."),"error");
					
				}				
			} else {
				//use default
				mode = "fastSync";
			}
		} else {
			//config not present
			//use defaults to set member values
			scripts = [];
			parent = document.getElementsByTagName('script')[0].parentNode;
			;
			mode = "fastSync";
		}
		//check to see if there are any scripts to load
		if(scripts.length > 0){
			//scripts need to be loaded
			switch(mode){
				case "sync":
					syncLoad(0,callback);
					break;
				case "fastSync":
					fastSyncLoad(callback);
					break;
				case "async":
					asyncLoad(callback);
					break;
				default:
				//error, invalid mode
				callback(new Error(mode + " is not a valid mode. Valid modes are sync,fastSync,and async."),"error");
			}
		} else {
			//no scripts to load
			callback(null,"scriptLoader finished");
		}
		
	}
	function attachInit(){
		if(document.addEventListener){
			//Modern
			document.addEventListener("DOMContentLoaded",init);
		} else {
			//Old IE
			if(document.attachEvent){
				document.attachEvent("onreadystatechange",function(){
					if (document.readyState === "interactive") {
						document.detachEvent("onreadystatechange", arguments.callee);
						init();
					}
				});
			} else {
				//use fallback
				oldOnload = window.onload;	
				window.onload = function(){
					oldOnload && oldOnload();
					init();
				};
			}
		}	
	}
	function fastSyncLoad(callback){
		var 	i,
				max = scripts.length,
				req = [],
				done = -1,
				script;				
		for(i = 0; i < max; i++){
			req[i] = new XMLHttpRequest();
			req[i].reqId = i;
			req[i].addEventListener("load",function(){
				load(this.reqId,this.responseText,callback);
			});
			req[i].open("GET",/*"/scriptLoader/"+ */scripts[i]);
			req[i].send();
		}
		function load(index,text,callback){
			var script;
			if(index - 1 == done){
				//create script
				script = createScript();
				script.text = text;
				appendScript(script);
				done++;
				if(done +1 == max){
					//done
					callback(null,"loaded");
				}
			} else {
				setTimeout(function(){
					load(index,text,callback);
				},10);
			}
		}		
	}
	function asyncLoad(callback){
		var max = scripts.length,
			done = 0,
			i,
			script;
		for(i = 0; i < max; i++){
			script = createScript(scripts[i]);
			addCallback(script,function(){
				done++;
			});
			appendScript(script);
			
		}
		asyncCheckDone(callback);
		function asyncCheckDone(callback){
			if(done == max){
				callback(null,"loaded");
			} else {
				setTimeout(function(){
					asyncCheckDone(callback);
				},5);
			}
		}
		
	}
	function syncLoad(start,callback){
		var max = scripts.length,
			doneMax = done.length,
			i;
		
		if(start >= max){
			//all scripts done
			callback(null,"loaded");			
		} else {
			//script not loaded yet, load it
			//create script element
				var script = createScript(scripts[start]);
				//add callback
				addCallback(script, function(){
					done.push(scripts[start]);
					syncLoad(start + 1,callback);
				});
				//add script to dom
				appendScript(script);				
			
		}
	}
	function loadFile(src,callback){
		var script = createScript(src);
		addCallback(script,callback);
		appendScript(script);
	}
	function loadText(scriptText,callback){
		var script = createScript();
		script.text = scriptText;
		addCallback(script, callback);
		appendScript(script);
	}
	function createScript(src, id){
		var script = document.createElement('script');
		script.type = "text/javascript";
		if(id){
			script.id = id;
		}
		if(src){
			script.src = src;
		}		
		return script;
	}
	function addCallback(script,callback){
		script.onload = function(){
			callback(null,"loaded");
		};
		return true;
	}
	function appendScript(script){
		parent.appendChild(script);
		return true;
	}
	function isArray(obj){
		return Object.prototype.toString.call(obj) === '[object Array]';
	}
	function isValidUrl(url){
		
	}
}