When to use async false and async true in ajax function in jquery

Question

When to use use async false or async true in an ajax call  In terms of performance does it make any difference     example       ajax           url   endpoint          type    post           async   false          success   function data                    if  i  1                     getMetricData data                    else if  i  2                                        capture   data

User · Answer

When async setting is set to false  a Synchronous call is made instead of an Asynchronous call  When the async setting of the jQuery AJAX function is set to true then a jQuery Asynchronous call is made  AJAX itself means Asynchronous JavaScript and XML and hence if you make it Synchronous by setting async setting to false  it will no longer be an AJAX call  for more information please refer this link

User · Answer

It s not relative to performance     You set async to false  when you need that ajax request to be completed before the browser passes to other codes    lt script gt                   ajax     async  false          Hey browser  first complete this request                                        then go for other codes        ajax          Executed after the completion of the previous async false request   lt  script gt

User · Answer

In basic terms synchronous requests wait for the response to be received from the request before it allows any code processing to continue  At first this may seem like a good thing to do  but it absolutely is not  As mentioned  while the request is in process the browser will halt execution of all script and also rendering of the UI as the JS engine of the majority of browsers is  effectively  single-threaded  This means that to your users the browser will appear unresponsive and they may even see OS-level warnings that the program is not responding and to ask them if its process should be ended  It s for this reason that synchronous JS has been deprecated and you see warnings about its use in the devtools console  The alternative of asynchronous requests is by far the better practice and should always be used where possible  This means that you need to know how to use callbacks and or promises in order to handle the responses to your async requests when they complete  and also how to structure your JS to work with this pattern  There are many resources already available covering this  this  for example  so I won t go into it here  There are very few occasions where a synchronous request is necessary  In fact the only one I can think of is when making a request within the beforeunload event handler  and even then it s not guaranteed to work  In summary  you should look to learn and employ the async pattern in all requests  Synchronous requests are now an anti-pattern which cause more issues than they generally solve

User · Answer

It is best practice to go asynchronous if you can do several things in parallel  no inter-dependencies   If you need it to complete to continue loading the next thing you could use synchronous  but note that this option is deprecated to avoid abuse of sync   jQuery ajax   method  39 s async option deprecated  what now

User · Answer

ShowPopUpForToDoList  function  id  apprId  tab        var snapShot    isFromAlert       if  tab     Request           snapShot    isFromTodoList         ajax           type   GET           url  common GetRootUrl  ActionForm SetParamForToDoList            data    id  id  tab  tab            async false          success  function  data                ActionForm EditActionFormPopup id  snapShot                          Here SetParamForToDoList will be excecuted first after the function ActionForm EditActionFormPopup will fire

[ajax] When to use async false and async true in ajax function in jquery

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