javascript – How to make code wait while calling asynchronous calls like Ajax-ThrowExceptions

Exception or error:

I am looking for something like this

function someFunc() {

callAjaxfunc(); //may have multiple ajax calls in this function
someWait(); // some code which waits until async calls complete
console.log('Pass2');

}

function callAjaxfunc() {
  //All ajax calls called here
  console.log('Pass1');

}

What I have tried?

1
Jquery.when()

tried using it..it works fine. But not the way I want. $.when will wait but the code next to $.when() runs with out waiting. The code inside do callback only runs after ajax calls

2.
setTimeOut() with a global flag

I was so confident this will work. I tried like following.

GlobalFlag = false;

function someFunc()     
    callAjaxfunc(); //may have multiple ajax calls in this function
    setTimeOut(waitFunc, 100); // some  which waits until async calls complete
    console.log('Pass2');
}

function callAjaxfunc() {
    //All ajax calls called here
    onAjaxSuccess: function() {
        GlobalFlag = true;
    };
    console.log('Pass1');    
}

function waitFunc() {
    if (!GlobalFlag) {
        setTimeOut(waitFunc, 100);
    }
}​

Still not able to get wanted result. Am I doing something wrong here? This is not the way?

Result I wanted should come like this

Pass1
Pass2

Not able to make any fiddle as it needs AJAX calls

EDIT: As many were suggesting callbacks..i know about them..but still the code next to somewait() will get executed…I want browser to completely stop executing code next to somewait() until the ajax call..Also it may be a bad practice but worth to know and try if possible…

How to solve:

Use callbacks. Something like this should work based on your sample code.

function someFunc() {

callAjaxfunc(function() {
    console.log('Pass2');
});

}

function callAjaxfunc(callback) {
    //All ajax calls called here
    onAjaxSuccess: function() {
        callback();
    };
    console.log('Pass1');    
}

This will print Pass1 immediately (assuming ajax request takes atleast a few microseconds), then print Pass2 when the onAjaxSuccess is executed.

###

Why didn’t it work for you using Deferred Objects? Unless I misunderstood something this may work for you.

/* AJAX success handler */
var echo = function() {
    console.log('Pass1');
};

var pass = function() {
  $.when(
    /* AJAX requests */
    $.post("/echo/json/", { delay: 1 }, echo),
    $.post("/echo/json/", { delay: 2 }, echo),
    $.post("/echo/json/", { delay: 3 }, echo)
  ).then(function() {
    /* Run after all AJAX */
    console.log('Pass2');
  });
};​

See it here.


UPDATE

Based on your input it seems what your quickest alternative is to use synchronous requests. You can set the property async to false in your $.ajax requests to make them blocking. This will hang your browser until the request is finished though.

Notice I don’t recommend this and I still consider you should fix your code in an event-based workflow to not depend on it.

###

Real programmers do it with semaphores.

Have a variable set to 0. Increment it before each AJAX call. Decrement it in each success handler, and test for 0. If it is, you’re done.

###

If you need wait until the ajax call is completed all do you need is make your call synchronously.

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