AJAX Get and Post methods (sending requests to the server)

Last Update:2016-02-24 Source: Internet

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To send the request to the server, we use the open () and send () methods of the XMLHttpRequest object:

Method	Description
Open (method,url,async)	Specifies the type of request, the URL, and whether the request is processed asynchronously. method: type of request; GET or POST URL: The location of the file on the server Async: True (asynchronous) or false (synchronous)
Send (string)	Sends the request to the server. string: only for POST requests

Method

Description

Open (method,url,async)

Specifies the type of request, the URL, and whether the request is processed asynchronously.

method: type of request; GET or POST
URL: The location of the file on the server
Async: True (asynchronous) or false (synchronous)

Send (string)

Sends the request to the server.

string: only for POST requests

GET is simpler and faster than POST, and can be used in most cases.
However, use the POST request in the following cases:
Unable to use cache file (update file or database on server)
Send a large amount of data to the server (POST has no data volume limit)
Post is more stable and more reliable than GET when sending user input with unknown characters

Get Method Example:

1 <HTML>2 <Head>3 <Scripttype= "Text/javascript">4 functionLoadxmldoc ()5 {6 varXMLHTTP;7 if(window. XMLHttpRequest)8   {//code for ie7+, Firefox, Chrome, Opera, Safari9 XMLHTTP=NewXMLHttpRequest ();Ten   } One Else A   {//code for IE6, IE5 - XMLHTTP=NewActiveXObject ("Microsoft.XMLHTTP"); -   } the Xmlhttp.onreadystatechange=function() -   { -   if(Xmlhttp.readystate==4 &&Xmlhttp.status== $) -     { + document.getElementById ("mydiv"). InnerHTML=Xmlhttp.responsetext; -     } +   } A Xmlhttp.open ("GET","/ajax/demo_get.asp",true); at xmlhttp.send (); - } - </Script> - </Head> - <Body> -  in <H2>Ajax</H2> - <Buttontype= "button"onclick= "Loadxmldoc ()">Request data</Button> to <DivID= "Mydiv"></Div> +  - </Body> the </HTML>

In the example above, it is possible to get the results of the cache.
To avoid this situation, add a unique ID to the URL:

1 xmlhttp.open ("GET", "demo_get.asp?t=" + math.random (), true);

2 xmlhttp.send ();

If you want to send information through the GET method, add information to the URL:

1 xmlhttp.open ("GET", "Demo_get2.asp?fname=bill&lname=gates", true);

2 xmlhttp.send ();

Post Method Ibid.

Example:

1 xmlhttp.open ("POST", "demo_post.asp", true);

2 xmlhttp.send ();

If you need to POST data like an HTML form, use setRequestHeader () to add an HTTP header. Then specify the data you want to send in the Send () method:

Method	Description
setRequestHeader (header,value)	Adds an HTTP header to the request. header: Name of the specified header Value: The values of the specified header

Method

Description

setRequestHeader (header,value)

Adds an HTTP header to the request.

header: Name of the specified header
Value: The values of the specified header

code example:

1 xmlhttp.open ("POST", "ajax_test.asp", true);

2 xmlhttp.setrequestheader ("Content-type", "application/x-www-form-urlencoded");

3 xmlhttp.send ("Fname=bill&lname=gates");

Asynchronous-True or False?
AJAX refers to asynchronous JavaScript and XML (asynchronous JavaScript and XML).
The async parameter of the open () method must be set to True if the XMLHttpRequest object is to be used for AJAX, or false.

When using Async=false, do not write the onreadystatechange function-put the code behind the Send () statement:

1 xmlhttp.open ("GET", "Test1.txt", false);

2 xmlhttp.send ();

3 document.getElementById ("mydiv"). Innerhtml=xmlhttp.responsetext;

AJAX Get and Post methods (sending requests to the server)

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