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

[Ori Volfovitch]

Not sure what you mean.
You just removed the .catch(), which means you do not handle in case of rejection.

[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.

[Ori Volfovitch]

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

Thanks!

[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)

[Ori Volfovitch]

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

[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

[Ori Volfovitch]

Nice combo.
So you are actually chaining them asynchronously?

[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

[Ori Volfovitch]

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

[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.

[Joel Ruiz]

You can chain the Promises. Inside of .then(), you can return another promise and it'll let you add another .then() underneath. You add a single .catch() at very end, which will work for all the .then() chains.

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