let synchronous code wait an asynchronous call

Question

I have a form of which I catch the submit event. I have to wait for a $.post call in order to decide whether to submit it. I've tried this:

$('#my_form').submit(function(event){
 var data = null;
 $.post("/post/call").then(function(_data){
 data = _data;
 });
 if ( $.isPlainObject(data) && data.status === 'ko' ) {
 return false; // Do not submit the original form
 } else {
 // Submit the original form
 }
});

But data results to be always null, also if _data is valorized, because $.post is an asynchrounous call. How can I wait for the $.post call to be completed?

EDIT: As wrote in the comments, I would like to avoid $.ajax({async: true}), because it freezes the page; is there any way to get the same effect without freezing the page?

• Felix Kling: possible duplicate of Synchronous calls with jquery
• Danny: Why not just put what you want to wait to do at the end async callback?
• Sven Bieder: where do you get then .then() from. a callback function gets attached in the post with a comma. your if must also be in the callback, because data is not set before the post is completed.
• kirilloid: Use synchronous call as Felix Kling advised. Everything, available with $.post is as well available via $.ajax
• mdesantis: I would like to avoid $.ajax({async: true}) , because it freezes the page; is there any way to get the same effect without freezing the page?

Answer 1

You should have some sort of flag that says the form is to be submitted or not as well as that the ajax is processing. Then when the ajax call passes, call $('#my_form').submit() to send the form.

Loosely,

var validated = false;
$('#my_form').submit(function(event){
 if (validated) {
 return true;
 }
 $.post("/post/call").then(function(_data){
 var data = _data;
 if ( $.isPlainObject(data) && data.status === 'ko' ) {
 // Do not submit the original form
 } else {
 validated = true;
 $('#my_form').submit();
 }
 });
 return false;
});

• Felix Kling: You probably should add another flag which indicates whether a call is in progress.

Answer 2

If you are using MVC / C#, and can use a Json request to access your web service, know the following.

$.getJSON

Is asynchronous

SOLUTION: $.ajax 

Can be set to synchronous