javascript动态创建script，并监听onload、onerror

var oScript = document.createElement('script');
    oScript.type = 'text/javascript';
    oScript.src = "xx.js";
    /*
    ** script标签的onload和onreadystatechange事件
    ** IE6/7/8支持onreadystatechange事件
    ** IE9/10支持onreadystatechange和onload事件
    ** Firefox/Chrome/Opera支持onload事件
    */

    // 判断IE8及以下浏览器
    var isIE = !-[1, ];
    if (isIE) {
        oScript.onreadystatechange = function () {
            //ie 即使404readyState也是loaded或complete
            if (this.readyState == 'loaded' || this.readyState == 'complete') {
                callback();
            }
        }
    } else {
        // IE9及以上浏览器，Firefox，Chrome，Opera
        oScript.onload = function () {
            callback();
        }

      oScript.onerror = function () {
          //error callback
        }

} 
 var head = document.getElementsByTagName('head')[0];
 head.appendChild(oScript);