jquery Ajax synchronous and asynchronous attributes async detailed

Example 1. jquery+ajax/"target=" _blank ">jquery Ajax sync Way

The code is as follows	Copy Code
$.ajax ({ URL: ' test.php ', Type: ' Post ', Async:false,//Using synchronous method, True is asynchronous Data: {' act ': ' Addvideo ', ' videoname ': videoname},//uses JSON objects here Success:function (data) { Code here ... }, Fail:function () { Code here ... } });

Example 2

code is as follows

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//javascript Function test () {  var a= 1;  $.ajax ({ br>   type  : ' Get ',   url   : ' test.php ',   data   : ' page=112 ',   success:function (msg)   {    alert (msg) ;    a= msg;   }  })  alert (a); } //test.php Sleef (' 5 ');//Rest five minutes echo ' in '; /*   This program is running   first print 1 (a=1) then five seconds later print in   According to this situation can know the AJAX implementation process of jquery   because it is asynchronous call &nb SP; Assign a value to a variable   it's wrong to do it anyway. Finally found this problem   parameter async to False for synchronous calls when Ajax returns results after the program continues */

Example 3

In this case, the default set value of Async is true, which is asynchronous, that is, when Ajax sends a request, the foreground will continue to execute the script behind the AJAX block until the server side returns the correct result before it executes the success , which means that the two threads are executed at this time, and the AJAX block emits a script (another thread) after the request followed by a thread and an AJAX block:

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$.ajax ({ Type: "POST", URL: "Venue.aspx?act=init", DataType: "HTML", Success:function (Result) {//function1 () F1 (); F2 (); } Failure:function (Result) { Alert (' Failed '); }, } Function2 ();

In the example above, when the Ajax block makes a request, he stays function1 () and waits for the server to return, but at the same time (during the wait), the foreground executes function2 (), that is, there are two threads at this time, We are here to say Function1 () and function2 ().

When the Asyn is set to False, it is synchronized when the AJAX request is made, that is, when the Ajax block makes a request, he waits in the function1 () and does not perform function2 (), knowing that the function1 () part of the execution is complete.

Attention

Synchronization means that when the JS code is loaded into the current Ajax will put all the code in the page to stop loading, the page out of suspended animation, when this Ajax execution will continue to run the other code page suspended animation state.
and asynchronous, the Ajax code runs as well as other code.
The Async:false of jquery, this property