As you have seen in previous posts, a promise in JavaScript represents the result of a task, which may or may not have completed yet. Or in simpler words, what to expect for a JavaScript call.
Q was designed to provide a robust way to provide you ways to write asynchronous code cleanly.
You can integrate the robustness of Q with jQuery promises.
Why Q?
As you learned in Asynchronous JavaScript Promises Using Q , you get additional goodness by using Q rather than jQuery’s promises. The main features being:
- Exception handling
- Several additional methods give you deep control of the promise
- An error (or in a promise reject) in one chained thens will be handled “down the chain” by a later
Q with jQuery
When you pass in jQuery into Q, it coerces the jQuery promise into a Q promise that you can then use.
The following code snippet returns a Q promise from a jQuery AJAX or jQuery getJSON call.
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| var qPromise = Q($.getJSON("data/products.txt")) | |
| .then(function (products) { | |
| $("#products").text(JSON.stringify(products)); | |
| }); |
You can continue to chain the promise and get all the goodness of Q.
Sample Code
You can get sample code for this post in the DevDays GitHub repository: https://github.com/devdays/object-javascript/tree/master/Q