动态加载jQuery的两种方法实例分析

function withjQuery(callback) { if(!(window.jQuery)) { var js = document.createElement('script'); js.setAttribute('src', 'https://dynamic.12306.cn/otsweb/js/common/jquery-1.4.2.min.js?version=5.47'); js.setAttribute('type', 'text/javascript'); js.onload = js.onreadystatechange = function() {  if (!this.readyState || this.readyState === 'loaded' || this.readyState === 'complete') {    if(callback && typeof callback === "function") {     callback();    }   js.onload = js.onreadystatechange = null;  } }; document.getElementsByTagName('head')[0].appendChild(js); }}withjQuery(  function() {   $(function(){ alert("jQuery loaded"); })();  });

// ==UserScript== // @name   12306 Booking Assistant// @version  1.4.0// @author  zzdhidden@gmail.com// @namespace https://github.com/zzdhidden// @description 12306 订票助手之(自动登录，自动查票，自动订单)// @include  *://dynamic.12306.cn/otsweb/*// @require https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js// ==/UserScript== function withjQuery(callback, safe){ if(typeof(jQuery) == "undefined") {  var script = document.createElement("script");  script.type = "text/javascript";  script.src = "https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js";  if(safe) {   var cb = document.createElement("script");   cb.type = "text/javascript";   cb.textContent = "jQuery.noConflict();(" + callback.toString() + ")(jQuery, window);";   script.addEventListener('load', function() {    document.head.appendChild(cb);   });  }  else {   var dollar = undefined;   if(typeof($) != "undefined") dollar = $;   script.addEventListener('load', function() {    jQuery.noConflict();    $ = dollar;    callback(jQuery, window);   });  }  document.head.appendChild(script); } else {  setTimeout(function() {   //Firefox supports   callback(jQuery, typeof unsafeWindow === "undefined" ? window : unsafeWindow);  }, 30); }}withjQuery(function($, window){ $(function() { alert("jQuery loaded"); })();}, true);