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

The following is an asynchronous submission of the user name (after entering the user name, the asynchronous submission will be judged by the background, and the front desk will immediately prompt whether it has been registered, and it will be judged when there is no need to submit!)

Submit by GET method

xx.html

<script type="text/javascript">
window.onload=function(){
  document.getElementById(&#39;username&#39;).onblur=function(){
    var name=document.getElementById(&#39;username&#39;).value;
    var req=new XMLHttpRequest();
    req.open(&#39;get&#39;,&#39;4-demo.php?name=&#39;+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
  }
}
</script>

Username:

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

xx.php

<?php
print_r($_GET);
?>　

1. IE does not support Chinese

2. =, & are confused with the keywords of the requested string.

POST submission

xx.html

<script type="text/javascript">
window.onload=function(){
  document.getElementById(&#39;username&#39;).onblur=function(){
    var name=document.getElementById(&#39;username&#39;).value;
    name=encodeURIComponent(name);
    var req=new XMLHttpRequest();
    req.open(&#39;post&#39;,&#39;5-demo.php?age=&#39;+20);
    req.onreadystatechange=function(){
      if(req.readyState==4 && req.status==200){
        alert(req.responseText);
      }
    }
  req.setRequestHeader(&#39;Content-Type&#39;,&#39;application/x-www-form-urlencoded&#39;);
    req.send(&#39;name=&#39;+name);  
  }
}
</script>

Username:

xx.php

<?php
print_r($_POST);
print_r($_GET);
?>

1. Send data through send()

2. SetRequestHeader() must be set to The passed parameters are converted into XML format

3. Post submission can directly submit Chinese without transcoding

4. The characters in the post request will also be consistent with the & and = characters in the URL. Confused, so it is recommended to use encodeURIComponent() encoding

5. At the same time as POST submission, you can submit GET

Solution

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

Just encode in js through encodeURIComponent().

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
  }
}

1. req.responseText: Get the returned string

2. req.responseXML: Get the returned data according to the DOM structure

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

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