JavaScript: load-async.js

load-async.js

/**
 * From: http://coolshell.cn/articles/9749.html
 **/

function cachejs(script_filename){
    var cache = document.createElement('object');
    cache.data = script_filename;
    cache.id = "coolshell_script_cache_id";
    cache.width = 0;
    cache.height = 0;
    document.body.appendChild(cache);
} 

function loadjs(script_filename) {
    var script = document.createElement('script');
    script.setAttribute('type', 'text/javascript');
    script.setAttribute('src', script_filename);
    script.setAttribute('id', 'coolshell_script_id');

    script_id = document.getElementById('coolshell_script_id');
    if(script_id){
        document.getElementsByTagName('head')[0].removeChild(script_id);
    }
    document.getElementsByTagName('head')[0].appendChild(script);
}

function LoadJS(){
    var script = './alert.js';
    loadjs(script);
}

cachejs('./alert.js');

<div class="btn" onclick="LoadJS()">Click to load alert.js </div>


// From: http://bbs.html5cn.org/thread-1177-1-8.html

function loadScript(url, callback) {
    var script = document.createElement("script");
    script.type = "text/javascript";

    //IE
     if (script.readyState) {
         script.onreadystatechange = function () {
             if (script.readyState == "loaded" || script.readyState == "complete") {
                 script.onreadystatechange = null;
                 callback();
             }
         }
     } else {
         //非IE
         script.onload = function () {
             callback();
         }
     }
     script.src = url;
     document.getElementById("head").appendChild(script);
    }
    //第一步加载jquery类库
    loadScript("jquery/jquery-1.4.1.js", function () {
     //第二步加载hello.js
     loadScript("js/hello.js", function () {
         //第三步加载world.js
         loadScript("js/world.js", function () {
    
         });
     });
});