What is the role of async in ajax

Async in ajax is used to set the execution of scripts in asynchronous or synchronous mode; when the async attribute value is true by default, it is asynchronous mode. After "$.Ajax" is executed, the script following ajax will continue to be executed. When its attribute value When set to false, the synchronous request will lock the browser, and other user operations must wait for the request to be completed.

The operating environment of this article: windows10 system, javascript1.8.5&&html5 version, Dell G3 computer.

What is the role of async in ajax

async. The default is true, which is asynchronous mode. After $.Ajax is executed, it will continue to execute. The script behind ajax triggers the success method in $.Ajax until the server returns data. At this time, two threads are executed. If you set it to false, all requests are synchronous requests. Before returning a value, synchronous requests will lock the browser, and the user must wait for the request to complete other operations before they can be executed.

Check out an example below:

var temp;
$.ajax({
async: false,
type : "POST",
 url : defaultPostData.url,
  dataType : 'json',
   success : function(data) 
   {
       temp=data;
    }
 });
 alert(temp);

This ajax request is a synchronous request, and alert(temp) will not be executed until there is no return value.

If async is set to: true, it will not wait for the result returned by the ajax request, but will directly execute the statement following ajax.

However, for the above method of setting synchronous requests, some netizens once reported that after setting async to false, the original intention was to return the data and then execute the script behind $.Ajax. Unexpectedly, this place caused the problem in Firefox. A splash screen appears under the browser (Firefox 11.0), and ajax is triggered when the scroll bar is pulled down to the bottom. In the end, you can only comment out async:false, that is, when async is true, you successfully solved the problem of the Firefox browser scroll bar being pulled down to the bottom and triggering ajax to appear as a splash screen.

[Related tutorial recommendations: AJAX video tutorial]

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