How to Ensure $.when() Waits for All Deferred Tasks in an Array?

Passing an Array of Deferreds to $.when()

Question:

Consider the following code where a list of deferred tasks is created:

var deferreds = getSomeDeferredStuff();

$.when(deferreds).done(function() { console.log("All done!") });

However, "All done!" is logged before all deferred tasks are completed. How can you pass an array of deferreds into $.when() and ensure that it waits for all tasks to finish?

Answer:

To pass an array of values to a function that expects separate parameters, use Function.prototype.apply:

$.when.apply($, deferreds).then(function() { console.log("All done!") });

Here's a breakdown of the code:

• $.when.apply($, deferreds): Spreads the deferreds array into separate arguments for $.when().
• then(function): Attaches a handler that runs when all deferreds are resolved.

Alternatively, in ES6 and newer, you can use the spread operator:

$.when(...deferreds).then(function() { console.log("All done!") });

In either case, the handler will receive an array of results, one for each deferred. Process this array to obtain the values you need.

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