Using $.when() with a variable array of functions

Question

I'd like to use when() to control finishing of multiple AJAX calls such as:

$.when(
    $.ajax( "test.aspx" ),
    $.ajax( "test2.aspx" ),
    ...
).then(...);

Finally I would like to use $.when with results of function calls from a variable array. I don't realize how.

How can we correct the next construction? The problem it's incorrect because we pass an array of Function objects, but not results of function calls.

funcArray = [ 
    function() { return $.ajax( "test.aspx" ) }, 
    function() { return $.ajax( "test2.aspx" ) }
]

if( cond )
{
    funcArray.push( function() { return $.ajax( "test3.aspx" ) } )
}

$.when.apply( null, funcArray ).then(...); // how to correct here and probably somewhere else?

Your functions have to return the result of $.ajax(): function() { return $.ajax( "test.aspx" ) } — ComFreek
– ComFreek, Commented Jan 25, 2014 at 16:32
@ComFreek I suppose it's a good correction but it's not the solution, isn't it? — sergzach
– sergzach, Commented Jan 25, 2014 at 16:35
$.when accepts promises as its arguments, not functions returning promises. You'll first need to call all your functions, store the returned promises in an array and pass that array to $.when (using apply). — Mattias Buelens
– Mattias Buelens, Commented Jan 25, 2014 at 16:41

Community · Accepted Answer · 2017-05-23 12:28:37Z

2

As Mattias Buelens already said in a comment, the problem is that you pass functions returning promises to $.when – not the actual promises.

You have to iterate the array and return the result of each function call.

There are several ways to do so:

[Most stable] Using jQuery's $.map function:

$.when.apply(null, $.map(funcArray, function (val) {
    return val();
  })
);

Using Array.prototype.map():

$.when.apply(null, funcArray.map(function (val) {
    return val();
  })
);

Firefox ≥ 22 also allows a so-called syntax of arrow functions:
```
$.when.apply(null, funcArray.map(fun => fun()));
```

edited May 23, 2017 at 12:28

CommunityBot

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answered Jan 25, 2014 at 16:42

ComFreek

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1 Comment

Mattias Buelens Over a year ago

If compatibility is an issue, you can also use $.map(array, func) to replace array.map(func).

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