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Discussion on: All (or just most) of what you need to know about handling Promises

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karataev profile image
Eugene Karataev

Yeah, as Joel mentioned, you can return promises to get one flat promise chain.
Imagine that you have 4 promises. If you follow example 1 in your post, you'll get promise structure like callback hell, but if you return next promise in every then, you'll get nice and flat promise chain.

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orivolfo profile image
Ori Volfovitch Author

Oh, now I understand.
Wow, this is worth editing the original post!

Thanks!

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efishtain profile image
efi shtain

Another improvement you can make is not using anonymous function
It gives you testability and readability
So instead of:

longPromise()
.then((data)=>{
console.log(data); // logs: longPromise resolved
return shortPromise();
.then((data)=>{
console.log(data) // logs: shortPromise resolved
})
.catch((error)=> {
console.log(error);
})
});

you can do:
async function firstHandler(data){
console.log(data)
return shortPromise()
}

longPromise.then(firstHandler).then(console.log).catch(console.log)

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orivolfo profile image
Ori Volfovitch Author

But wouldn't this example start to get ugly if you had more that just 2 Promises?

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efishtain profile image
efi shtain

getData()
.then(processData)
.then(convertData)
.then(saveData)
.then(notifyOnSuccess)
.catch(handleError)

looks ok to me
any how I'd go with async await today as much as I can, only use native promises if I need to wrap a callback from a library or something like that

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orivolfo profile image
Ori Volfovitch Author

Nice combo.
So you are actually chaining them asynchronously?

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efishtain profile image
efi shtain

what do you mean?
you can't processData before you got the data, so it has to be done in series
getData() has to return a promise, the rest of the functions would automatically be converted to async

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orivolfo profile image
Ori Volfovitch Author

So why in your firstHandler example did you made the function to be async?

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efishtain profile image
efi shtain

Optional.
If you use it elsewhere, and it is async, mark it as async.
only when I use anonymous function directly in the chain I won't mark methods with async unless I have to.