javascript高级知识四

/**
 动态加载js
*/
function loadScript(url,callback){
    //如果有该JS，则移出该JS
    var script=document.createElement('script');
    script.type='text/javascript';
    script.async='async';
    script.src=url;
    //该ID放入上方的判断内 
    script.id = "1"
    var head = document.head || document.getElementsByTagName('head')[0];
    head.appendChild(script);
    //或者放在body尾部document.body.appendChild(script);
    script.onload = script.onreadystatechange = function () {
        console.log("测试");
        if (!this.readyState || this.readyState == 'loaded' || this.readyState == 'complete') {
            script.onreadystatechange=null;
            callback();
        }
        script.onload = script.onreadystatechange = null;
    }
}

// 使用