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This article mainly explains "how to use AJAX". The content in the article is simple and clear, and it is easy to learn and understand. Please follow the editor's ideas to study and learn how to use AJAX.

What is a server: our page comes from the server; the instance (stores a page on the phpnwo)

We put the page on the server of the Internet and have our own website.

1. Asynchronous synchronization

Synchronization in life:

Asynchronism in life:

In the JavaScript language, the concepts of synchronization and asynchrony are just the opposite.

Synchronization in this JavaScript is: if you don't execute the above code, then don't execute the following code; step by step, this is synchronization.

Asynchronism is code that can be executed together.

The concept of process

Process ≠ program from the beginning to the end of an execution process is called a process, multiple branches of the program running at the same time, called thread multi-thread asynchronous execution, can improve the efficiency of the program.

The importance of AJAX

In the eyes of many companies, the proficiency in using AJAX = your work experience.

two。 What is AJAX?

Ajax is an important means of data exchange between front and back end.

The full name of Ajax is "Asynchronous JavaScript and XML" (Asynchronous JavaScript and XML). It is not a single technology of JavaScript, but a combination of a series of technologies related to interactive web applications. With Ajax, we can update the page without refreshing status, and implement asynchronous submission, which improves the user experience.

I. Overview of Ajax

The concept of Ajax was invented by JesseJamesGarrett in 2005. It is not a single technology in itself, but a collection of technologies, mainly including:

1.JavaScript, capturing interactive behavior through users or other browser-related events

2.XMLHttpRequest object, which allows you to send requests to the server without interrupting other browser tasks

3. A file on the server that saves text data in XML, HTML, or JSON format

4. Other JavaScript, interpret the data from the server (such as the data obtained by PHP from MySQL) and render it to the page.

Because Ajax contains many features, its advantages and disadvantages are also very obvious. The main advantages are as follows:

1. No plug-in support is required (general browsers and JavaScript enabled by default)

two。 Excellent user experience (updatable data can be obtained without refreshing the page)

3. Improve the performance of Web programs (relax on demand in passing data without having to submit as a whole)

4. Reduce the burden on the server and bandwidth (transfer some operations from the server to the client)

The shortcomings of Ajax are as follows:

1. Different versions of browsers have insufficient support for XMLHttpRequest objects (for example, before IE5)

two。 The forward and backward functions are destroyed (because Ajax is always on the current page, there is no chance of front and back pages)

3. Search engines are not supported enough (because search engine crawlers do not yet understand the content of data changes caused by JS)

4. Lack of development and debugging tools (JS or Ajax debugging development is pitifully rare compared to the toolset of other languages).

The use of 3.AJAX

The order of answering and making calls:

1. First of all, there must be a phone call.

two。 Dial a number

3. Talk.

4. Listen to the message on the other side of the phone

/ / there is a phone: create a request object

1.var AJAX=new XMLHttpRequest ()

/ / dialing: set request parameters

2.AJAX.open ('get','data/test.json',true)

The first parameter: POST | | GET

The difference between POST and GET

POST is to send data, GET is to receive data

The security of sending data in PSOT is better than that in GET.

There is no limit on the size of the data sent by POST, while the size of GET is limited to 2mm 100k.

When to use GET and POST: use GET when getting data, and POST when manipulating data.

The third parameter: when the Boolean value is true, the server request is made asynchronously, that is, the script does not wait after executing the send () method

The execution result of the server, but continues to execute the script code

When the Boolean value is false, the server request is made synchronously, that is, the script waits after executing the send () method

The return of the execution result of the server, if it times out during the waiting process, it will no longer wait and continue to execute the following script code!

Ajax.onreadystatechange = function ()

{

If (ajax.readyState = = 4 & & ajax.status = 200) {func_succ (ajax.responseText);} else {/ / alert ("ajax faild readyState:" + ajax.readyState+ "status:" + ajax.status);}

}

4.ajax.send (null)

Ajax.readyStatus

0-(uninitialized) the send () method has not been called yet

1-(load) has called the send () method and is sending the request

2-(load completed) the send () method has been executed and all the response contents have been received.

3-(interactive) parsing response content

4-(complete) the parsing of the response content is complete and can be called on the client side.

Thank you for your reading, the above is the content of "how to use AJAX". After the study of this article, I believe you have a deeper understanding of how to use AJAX, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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