Detailed explanation of how to use ajax

AJAX is a technology for exchanging data with a server that updates part of a web page without reloading the entire page. 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 for using 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:

##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 convert the passed parameters into XML format

3. Post submission can directly submit Chinese, no need Transcoding

4, characters in

post request

will also be confused with the & and = characters in the URL, so it is recommended to also use encodeURIComponent() encoding5 , At the same time as POST submission, GET submission can be performed

Solution

IE does not support Chinese =, & is confused with the keywords of the requested string 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

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