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  之前了解过AJAX，最近用的比较多，又重新温习一下，简单整理了一下，文中的英文注释全是小编自翻，可能不对或者不够好的地方，欢迎大家指正！

/*** 什么是AJAX* 		异步JAVASCRIPT和XML（其中的A表示async,异步的）* @authors enlove (you@example.org)* @date    2017-11-30 10:06:03* @version $Id$*/function xmload(){var xmlhttp;if(window.new XMLHttpRequest){xmlhttp = new XMLHttpRequest();//create a object of XMLHttpRequest}else {xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");}xmlhttp.onreadystatechange = function(){if(xmlhttp.readyState == 4 && xmlhttp].status == 200){document.getElementById("enlove").innerHTML = xmlhttp.responseText;}}/***send HttpRequest to server*we can use the function of open and send*the params of open: the first param is the method of sending HttpRequest to server,*there are two methods, one is "GET", and another one is "POST"; the second param is *the url that you store your texts in your server; the last param whose type is boolean,*that true represent "async", false represent "sync"** attention: function of send(string) only can be used when the method is "POST"*/xmlhttp.open("GET","/try/ajax/enlove.txt",true);xmlhttp.send();
}/*** GET or POST*  	compare to POST, GET is faster and easier than POST, and GET can be used at most common,*  	but  please use POST at following:*  	*can not use cache(to update the file or DB on the server)*  	*send great amount of data(POST have no limit of data)*  	*send character that is unknown, POST is stable than GET*//*** above the following examples, the result is posssible caches* to avoid this, please add an unique ID to the url,like that */xmlhttp.open("GET","/try/ajax/enlove.txt?t="+Math.random(),true);xmlhttp.send();/*** if you want to send message by GET, please add information to URL*/xmlhttp.open("GET","/try/ajax/enlove.txt?name=Henty&value=ford",true);xmlhttp.open();/*** if you have necessary to POST data like form of HTML, please use setRequestHeader() to add* HTTP header. then add message that you want to send in function send.*/xmlhttp.open("GET","/try/ajax/enlove.txt",true);xmlhttp.setRequestHeader("content-type", "application/x-www-form-urlencoded");xmlhttp.send(name=Henty&value=ford);/*** for the developers of web, the AJAX is a big progress. It costs too much time to handle the masks on sever. Before AJAX, this can led to the applications stop or hang.* By AJAX, JavaScript have no need to wait the response from server, and *  * handle other javascripts when waiting sever's responses*  * handle the js when the response is done*//*** Async = true* when the last param of function open is true, please provision(规定) the response at onreadystatechange's stauts.*/xmlhttp.onreadystatechange = function(){if(xmlhttp.readyState == 4 && xmlhttp].status == 200){document.getElementById("enlove").innerHTML = xmlhttp.responseText;}}
/*** Async = false*/xmlhttp.open("GET","/try/ajax/ajax_info.txt",false);xmlhttp.send();document.getElementById("myDiv").innerHTML=xmlhttp.responseText;/*** the event of onreadystatechange* when the requests are sent to server, we need to handle some masks based on response* when the readystate changes, it will trigger the events of onreadystatechange* the attribute of readyState store the status of XMLHttpReuqest.* next is the important attributes of XMLHttpReuqest.*/________________________________________________________________________________attributes           |     description________________________________________________________________________________onreadystatechange   | when the readystate changes, it will trigger the events of  |onreadystatechange________________________________________________________________________________readyState          | store the status of new XMLHttpRequest, from 0 to 4|   0: the request is not intialization|   1: the connect to server is establish|	 2: the request is recieved|   3: the resquet is handling  |   4: the request is done, and response is onready________________________________________________________________________________status	             |  200: OK|  404: the pages are not found________________________________________________________________________________