javascript动态加载js脚本的代码

function require(url, options){
    var head, node, isOpera;
    isOpera         = typeof opera !== 'undefined' && opera.toString() === '[object Opera]';
    options.success = options.success || function(){};
    options.error   = options.error || function(){};
    options.type    = options.type || 'text/javascript';
    options.charset = options.charset || 'utf-8';
    options.async   = options.async || true;
    
    head            = document.getElementsByTagName("head")[0];
    node            = document.createElement(//javascript/i.test(options.type) ? 'script' : 'style');
    node.type       = options.type;
    node.charset    = options.charset;
    node.async      = options.async;
    node.src        = url;
    if (node.attachEvent &&
        !(node.attachEvent.toString && node.attachEvent.toString().indexOf('[native code') < 0) &&
        !isOpera){
        node.attachEvent('onreadystatechange', function(){
            if(!node.readyState || node.readyState == "loaded" || node.readyState == "complete"){
                options.success();
            }
        });
    }else{
        node.addEventListener('load', options.success, false);
        node.addEventListener('error', options.error, false);
    }
    
    head.appendChild(node);
}

require('http://code.jquery.com/jquery-1.7.3.min.js', {
    success:function(){
        alert('jquery loaded!');
    },
    error:function(){
        alert('jquery load fail!');
    }
});