javascript按顺序加载运行js方法

function loadJS(url){
  var Script = document.createElement('script');
  Script.setAttribute('src', url);
  Script.setAttribute('type', 'text/javascript');
  document.body.appendChild(Script);
  return Script;
}

loadJS('a.js');
loadJS('b.js');

function loadJS(url, success) {
      var domScript = document.createElement('script');
      domScript.src = url;
      success = success || function () {
          };
      domScript.onload = domScript.onreadystatechange = function () {
        if (!this.readyState || 'loaded' === this.readyState || 'complete' === this.readyState) {
          success();
          this.onload = this.onreadystatechange = null;
          this.parentNode.removeChild(this);
        }
      }
      document.getElementsByTagName('head')[0].appendChild(domScript);
    }

loadJS(getUrl('a.js'), function () {
      loadJS(getUrl('b.js'), function () {
        console.log('a.js ,b.js 加载完成');
      });
});