Ajax Knowledge Points

What is Ajax?

Ajax is a technique for exchanging data with a server and updating parts of a web page without reloading the entire page.

Ajax usage steps:

1. Create an asynchronous object

var xmlhttp=new XMLHttpResquest();

2. Set the request method and request address

xmlhttp.open("GET","test1.txt",true);

Specifies the type of request, the URL, and whether to process the request asynchronously.

method : the type of request; GET or POST
url : the location of the file on the server
async : true (asynchronous) or false (synchronous)

3. Send request

xmlhttp.send();

4. Monitor status changes

xmlhttp.onreadystatechange=function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status<300 || xmlhttp.status == 304)
    {
    console.log("接收到服务器返回的数据")；
    }
  }

Holds the state of the XMLHttpRequest. Varies from 0 to 4.

0: request is not initialized
1: server connection established
2: Request received
3: Request processing
4: The request is complete and the response is ready

5. Process the returned results

responseText	Get the response data as a string.
responseXML	Get the response data in XML form.

Problems with Ajax in IE browser:

1. Compatibility issues:

var xmlhttp;
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }

2. Cache problem:

In IE browser, if a GET request is sent through Ajax, then IE browser thinks that there is only one result for the same URL.

Solution: Add a random parameter to the url, such as time and random number. new Date(). getTime()

Five steps of Ajax request! ! !

Ajax Knowledge Points

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