Implement ajax to send asynchronous requests (graphic tutorial)
This article mainly teaches you how to easily implement ajax to send asynchronous requests, which has certain reference value. Interested friends can refer to
ajax sends asynchronous requests for your reference. The specific content is as follows
First step(Get XMLHttpRequest)
Ajax actually only needs to learn one object: XMLHttpRequest. If you master it, you will master ajax!!!
1. Get XMLHttpRequest
Most browsers support: var xmlHttp=new XMLHttpRequest();
IE6.0:var xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
IE5.0 uses earlier versions of IE: var xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
2. Write a function that creates an XMLHttpRequest object
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The second step(Open the connection with the server)
xmlHttp.open(): used to open the connection with the server, it requires Three parameters:
Request method: can be GET or POST
Requested URL: Specify the server-side resource, for example:/day23_1/AServlet
Whether the request is asynchronous: If true, it means sending asynchronously request, otherwise synchronous request
xmlHttp.open("GET","/day23_1/AServlet",true);//For example
Step Three(Send Request)
xmlHttp.send(null): If not given, some browsers may not be able to send!
Parameters: Yes Request body content! If it is a GET request, null must be given.
If it is a POST request, as follows
xmlHttp.send(“username=zhangSan&password=123”);
Four steps:
Register a listener on an event of the xmlHttp object: onreadystatechange
The xmlHttp object has a total of 5 states
0: Initialization is not completed, just created XMLHttpRequest object, the open() method has not been called yet
1: The request has started, the open() method has been called, but the send() method has not been called yet
2: The request is sent in completion status, the send() method has been called
3: Start reading the server response
4: End reading the server response (usually we only care about the last status!!!)
Get the status of the xmlHttp object
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Get the status code of the server response (200: Success 304: Status has not changed 404 500: Server error)
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Get the content of the server response
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So the listener should be written like this
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The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.
Related articles:
Ajax implementation of saving and reading uploaded images to the background (graphic tutorial)
Struts2 and Ajax data interaction (graphic tutorial)
The above is the detailed content of Implement ajax to send asynchronous requests (graphic tutorial). For more information, please follow other related articles on the PHP Chinese website!

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