// 動態插入script標簽
function createScript(url, callback){
var oScript = document.createElement('script');
oScript.type = 'text/javascript';
oScript.async = true;
oScript.src = url;
/*
** script標簽的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
*/

// 判斷IE8及以下瀏覽器
var isIE = !-[1,];
if(isIE){
alert('IE')
oScript.onreadystatechange = function(){
if(this.readyState == 'loaded' || this.readyState == 'complete'){
callback();
}
}
} else {
// IE9及以上瀏覽器，Firefox，Chrome，Opera
oScript.onload = function(){
callback();
}
}
document.body.appendChild(oScript);
}

createScript('xxx.js', function(){
console.log('OK');
});