动态加载脚本

loadscript.js

var loadScript = function (url, callback) {
      var script = document.createElement("script"),
          head = document.getElementsByTagName("head")[0];

      script.type = "text/javascript";
      // IE
      if (script.readyState) {
          script.onreadystatechange = function () {
              if (script.readyState === "loaded" || script.readyState === "complete") {
                  script.onreadystatechange = null;
                  callback && callback();
              }
          }
      } else {
          // Chrome, Firefox等
          script.onload = function () {
              callback && callback();
          }
      }

      script.src = url;
      head.appendChild(script);
  };