$LAB.setGlobalDefaults({Debug:true}) //打开调试
$LAB//第一个执行链.script('http://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.0/jquery.min.js').script('http://cdnjs.cloudflare.com/ajax/libs/lodash.js/2.4.1/lodash.min.js')//第二个执行链.wait(function(){// console.log(window.$)// console.log(window._)
    })//第三个执行链.script('http://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.1.1/js/bootstrap.min.js').script('http://cdnjs.cloudflare.com/ajax/libs/fancybox/2.1.5/jquery.fancybox.pack.js')//第四个执行链.wait(function(){// console.log(plugin1Function)// console.log(plugin2Function)
    })//第五个执行链.script('./module1.js').script('./module2.js')//第六个执行链.wait(function(){// console.log(module1Function)// console.log(module2Function)})

//这三个执行是并行加载完以后，执行的3个wait操作
驱动执行的函数advance_exec_cursor, chain length:2  exec_cursor:0 LAB.js:46
驱动执行的函数advance_exec_cursor, chain length:4  exec_cursor:0 LAB.js:46
驱动执行的函数advance_exec_cursor, chain length:6  exec_cursor:0 LAB.js:46
//因为request_script函数中setTimeout(f,0)，所以加载会滞后于wait操作
start script load (ordered async): http://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.0/jquery.min.js LAB.js:46
start script load (ordered async): http://cdnjs.cloudflare.com/ajax/libs/lodash.js/2.4.1/lodash.min.js LAB.js:46
start script load (ordered async): http://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.1.1/js/bootstrap.min.js LAB.js:46
start script load (ordered async): http://cdnjs.cloudflare.com/ajax/libs/fancybox/2.1.5/jquery.fancybox.pack.js LAB.js:46
start script load (ordered async): file:///D:/Users/sj_yu/Desktop/work/20140408/LABjs/./module1.js LAB.js:46
start script load (ordered async): file:///D:/Users/sj_yu/Desktop/work/20140408/LABjs/./module2.js LAB.js:46
script execution finished: http://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.0/jquery.min.js LAB.js:46
script execution finished: http://cdnjs.cloudflare.com/ajax/libs/lodash.js/2.4.1/lodash.min.js LAB.js:46
//按顺序执行完第一组执行链，也就是jquery和lodash，执行完JS后，调用advance_exec_cursor来探测执行游标是否需要移动
驱动执行的函数advance_exec_cursor, chain length:6  exec_cursor:0 LAB.js:46
//执行第二组执行链
$LAB.wait() executing: function (){// console.log(window.$)// console.log(window._)} LAB.js:46
//执行第三组执行链
script execution finished: http://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.1.1/js/bootstrap.min.js LAB.js:46
script execution finished: http://cdnjs.cloudflare.com/ajax/libs/fancybox/2.1.5/jquery.fancybox.pack.js LAB.js:46
//执行完第三组后，触发advance_exec_cursor
驱动执行的函数advance_exec_cursor, chain length:6  exec_cursor:2 LAB.js:46
//第四组执行链
$LAB.wait() executing: function (){// console.log(plugin1Function)// console.log(plugin2Function)} LAB.js:46
//第五组执行链
script execution finished: file:///D:/Users/sj_yu/Desktop/work/20140408/LABjs/./module1.js LAB.js:46
script execution finished: file:///D:/Users/sj_yu/Desktop/work/20140408/LABjs/./module2.js LAB.js:46
驱动执行的函数advance_exec_cursor, chain length:6  exec_cursor:4 LAB.js:46
//执行第六组执行链
$LAB.wait() executing: function (){// console.log(module1Function)// console.log(module2Function)} 

//核心代码
(function(global){function create_sandbox() {//加载脚本，用到的方式有document.createElement('script')，xhrfunction do_script() {//脚本加载if(需要预加载) {if(是否默认支持预加载) {if(是否支持preload属性) {script.preload = true;} else {script.onreadystatechage = function() {if (script.readyState == "loaded") onload();}}script.src = src;} else if(是否用XHR方式) {new XMLHttpRequest();} else {script.type = "text/cache-script";create_script_load_listener();script.src = src;}} else if(可以异步加载) {script.async = false; //强制同步执行
                create_script_load_listener();script.src = src;} else {create_script_load_listener();script.src = src;}}//创建执行链function create_chain() {var chain = [];//执行链//执行完JS调用该函数function chain_script_executed() {advance_exec_cursor();}//主动执行每个执行链function advance_exec_cursor() {while(执行游标 < chain.length) {if(执行链是wait中的函数) {执行wait函数} else if(该执行链还没执行完) {} 游标++;}if (游标 == chain.length) {执行停止}}//执行链apivar chainedAPI = {script: function() {do_script();return chainedAPI;//支持链式调用
                },wait: function() {if(arguments.length > 0) {chain.push(arguments)}advance_exec_cursor();return chainedAPI;//支持链式调用
                }}return {script:chainedAPI.script, wait:chainedAPI.wait};} //end of create_chain//整个$LAB的接口var instanceAPI = {script:function(){return create_chain().script.apply(null,arguments);},wait:function(){return create_chain().wait.apply(null,arguments);}};return instanceAPI;} // end of create_sandbox//create_sandbox()返回 instanceAPI,包含script，wait等接口global.$LAB = create_sandbox();
})(this);