Resolve jquery deferred object with another deferred object

Question

How to resolve one Deffered object with resolve state of another. Simple example and simple explanation please (saw a lot of difficult ones).

How I can resolve result promise with a foo(), without .done(..) and .fail(..)?

var result = $.Deferred();

/**
 * @returns {Deferred}
 */
var foo = function() {
  // ... something that returns deferred object at random moment of time
};

foo()
  .done(function(){result.resolve()})
  .fail(function(){result.reject()})
;

setTimeout(function() {
    result.reject();
}, 50);

setTimeout(function(){
    console.log('Result is:', result.state());
}, 100);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

it's more complex. foo function can be not allowed for modify, and result can be resolved in many other ways. But if foo has been resolved the very first, result should have that resolution of the foo. — i.Nemiro
– i.Nemiro, Commented May 7, 2015 at 14:06

dfsq · Accepted Answer · 2015-05-06 13:49:13Z

2

You can use function passed in $.Deferred and resolve/reject deferred from inside:

var result = $.Deferred(function() {
    Math.random() > 0.5 ? this.resolve() : this.reject();
});

setTimeout(function(){
    document.write('Result is: ' + result.state());
}, 100);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

edited May 6, 2015 at 13:49

answered May 6, 2015 at 13:41

dfsq

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1 Comment

Benjamin Gruenbaum Over a year ago

If we're being clever: var result = $.Deferred()[Math.random() > 0.5 ? "resolve" : "reject"]()

collapsar · Accepted Answer · 2015-05-06 14:11:56Z

1

Your Deferred object def is superfluous (see the links given by Benajmin Gruenbaum why it's actually dangerous [silent fails]). Resolve/reject the result object:

var result = $.Deferred();
var foo = function() {
  return Math.random() > 0.5 ? result.resolve() : result.reject();
};

setTimeout(function(){
    document.write('Result is:', result.state());
}, 500);

foo();

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

edited May 6, 2015 at 14:11

answered May 6, 2015 at 13:45

collapsar

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3 Comments

Benjamin Gruenbaum Over a year ago

This is called the deferred anti-pattern.

collapsar Over a year ago

@BenjaminGruenbaum Thanks for shedding light on an aspect of the code that was outside my focus. Answer adjusted.

Bergi Over a year ago

Resolving a result deferred that is defined outside of your foo function is actually even worse.

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