4 steps to teach you how to use AJAX

AJAX stands for "Asynchronous Javascript And XML" (Asynchronous JavaScript and XML), which refers to a web development technology for creating interactive web applications.

AJAX = Asynchronous JavaScript and XML (a subset of Standard Universal Markup Language).

AJAX is a technology for creating fast, dynamic web pages.

AJAX is a technology that can update parts of a web page without reloading the entire web page. [1]

By exchanging a small amount of data with the server in the background, AJAX can enable asynchronous updates of web pages. This means that parts of a web page can be updated without reloading the entire page.

Traditional web pages (not using AJAX) must reload the entire web page if the content needs to be updated.

This article mainly introduces the relevant knowledge about the use of AJAX.

AJAX is an asynchronous transmission, partial refresh is very convenient and has many uses!

First, there are 4 steps to use AJAX:

1. Create an AJAX object

var xmlHttp = new XMLHttpRequest();

2. Establish a connection ('submission method', 'Url address')

##xmlHttp.open('get','./ AJAX_XML.xml');

3. Determine ajax preparation status and status code

xmlHttp.onreadystatechange = function(){ if (xmlHttp.readyState==4 && xmlHttp.status==200) { } }

4. Send request

xmlHttp.send(null); //get method parameter is null, post method, the parameter is the submitted parameter

Submit by GET method

xx.html

< input type="text" name="" id="username">

xx.php

POST submission

xx.html

xx.php

IE does not support Chinese =, & and The keywords of the requested string are confusedProblem

window.onload=function(){ document.getElementById('username').onblur=function(){ var name=document.getElementById('username').value; name=encodeURIComponent(name); //编码 var req=new XMLHttpRequest(); req.open('get','4-demo.php?name='+name); req.onreadystatechange=function(){ if(req.readyState==4 && req.status==200){ alert(req.responseText); } } req.send(null); //如果send()方法中没有数据，要写null } }

Pay attention to the difference between post/get submission methods!

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