动态创建script标签,判断加载完成调用

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

var script = document.createElement('script');

script.type = 'text/javascript';

script.charset = 'utf-8';

script.onload = script.onreadystatechange = function() {

    if (!this.readyState || this.readyState === "loaded" || this.readyState === "complete" ) {

        callback();

        script.onload = script.onreadystatechange = null;

    }

};

script.src= url;

head.appendChild(script);