javascript - JavaScript：异步下载js，下载失败时如何调用错误函数

Question

一个常用的异步下载js函数如下。

但是当下载失败时，如何调用错误函数。

该函数将是：函数 loadScript(url, callback, errcb)。

function loadScript(url, callback){ 
    var script = document.createElement("script") 
    script.type = "text/javascript"; 
    if (script.readyState){ //IE 
        script.onreadystatechange = function(){ 
            if (script.readyState == "loaded" || script.readyState == "complete"){ 
                script.onreadystatechange = null; 
                callback(); 
            } 
         }; 
    } else { //Others: Firefox, Safari, Chrome, and Opera 
        script.onload = function(){ 
            callback(); 
        }; 
    } 
    script.src = url; 
    document.body.appendChild(script); 
}