JavaScript’s Deferred Promise Pattern

The deferred pattern is a great way to add new flexibility to the way you use promises.

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[andrew-burgess]

If you’ve used the deferred pattern before, share your use case in a comment!

[samuelgunter]

my initial thought was "what that's stupid" but through the example I thought "yeah that can be useful". this was because the way it originally seemed was that you returned the deferred object itself, and the caller of the function got back the promise as well as a way to resolve and a way to reject, but since you just return the promise it's just a more compact way to do it than you would with a promise

[kalelsoffspring]

I'm most a backend dev, but this is super handy even for certain asynchronous operations *I* would do. Love it!

[dimitrimitropoulos]

it'd be super cool to see more about what you're up to with the audio APIs!

[kerrykreiter]

Thank you so much for helping beginners advance their level of JS knowledge. Your top-level tutorials are always presented so clearly and concisely that even I can benefit.

[dennisk]

Super useful pattern for mocked promises in tests. Gives test full control of promise resolution or rejection

[oscardasilva]

Wow thank you, I wish you post more advanced content like this.

[hideinbush]

Would love seeming more patterns videos like this!

[tempaccount]

Hi @Andrew. This was a great topic and you did teach us well, but if you give us more use case for this, it would be better.

[deamorta]

This is really cool. Please more patterns!!

[EthanStandel]

I think that pattern makes your code way less readable when you could just say

const asyncBlob = new Promise(resolve => ...)

and wrap it around the media recorder stop event listener and then return asyncBlob in the returned function. I think using a plain promise here creates a more distinct point of definition for how the value of the blob gets resolved and what logic is required to resolve it.

This just feels like abstraction for the purpose of abstraction.

[thi-m]

Great video. I've never seen this pattern before. Thank you for sharing!

[magicbob]

This is super cool. Will be looking for ways to use it going forward!

[bahmanasheghi]

this is great, I used to to create a chainable promise returning Api call!

[Luxcium]

It's unusual for me to a actually use the code from a video including the most interesting and I have been learning a lot from many but it is the second time I am using the code from your video to play with it and such

[darealmexury]

I must say I never really cared about TypeScript that much, but the way you explain TypeScript and the possibilities / ease of use is making me interested.

[lierdakil]

There is a simple enough way to do this without this pattern, just wrap setting up the event handlers inside the promise, bind it to a variable, then start, and return your function returning the promise. Not to say this pattern isn't useful, but in my experience it's very occasionally useful for very convoluted async control flows.

[seannewell]

Yeah deferred rocks, it essentially encapsulates in a reusable way whenever I've done new Promise(.. and captures the resolve function by binding it to an outer variable. Deferred is way less to reason about.

[helsontaveras]

Love this pattern! I’m using something very similar with the spawn child API to capture the exit event. I need to know the return code, and that’s only available on exit callback.

[grerff]

I don't get it, where did you get that "Deferred" type from?