Microsoft/TypeScript

TypeScript is a superset of JavaScript that compiles to clean JavaScript output.

Gareth Jones

@G-Rath

no wait what

async is in my code

for a second I thought it was I'd just missed async, but nope: async is there

so your example doesn't really relate to mine, as far as I can tell

AnyhowStep

@AnyhowStep


function takesNumberOnly (x : number) {
  console.log(x+1);
}
async function returnPromise ()  {
  const x = await 1;
  takesNumberOnly(x);
  takesNumberOnly(await 1);
}

If (await 1) is an expression of type Promise<number>

Then the second call to takesNumberOnly would not work

Gareth Jones

@G-Rath

Yeah I see. and you're right; this is turning how I figured it would

it's contextual, but too complex to type like that

AnyhowStep

@AnyhowStep

It's sytactic sugar for,

function returnPromise2 ()  {
  Promise.resolve(1)
    .then((x) => {
      takesNumberOnly(x);
      Promise.resolve(1)
        .then((y) => {
          takesNumberOnly(y);
        });
    });
}

Gareth Jones

@G-Rath

yeah yeah

AnyhowStep

@AnyhowStep

gdi gitter highlighting

Gareth Jones

@G-Rath

you need to add ts

im actually slightly disppointed in myself for not putting that together XD

but cheers for the sanity check

AnyhowStep

@AnyhowStep

Sometimes, adding ts doesn't make it any better =x

No problem <3

Gareth Jones

@G-Rath

yeah I know

but so yeah: it's b/c of the await in the inner fn

also ugh ffs my whole fn is redundant XD which is annoying b/c I thought that originally :joy:

AnyhowStep

@AnyhowStep

I didn't even notice till you said it =x

I need to up my code review skillz

Bruce Pascoe

@fatcerberus

(await 1) is expression of type number

It auto-wraps 1 in a promise and then unwraps it

You basically just waited an extra tick for a value you already had :P

AnyhowStep

@AnyhowStep

Kick him down some more :soccer:

Derya Aydede

@Derya

is async/await actually just syntactic sugar?

i was under the impression that it actually is not the exact same as the non-async equivalent

AnyhowStep

@AnyhowStep

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/await#Description

Without await, promises in for loops would be a hassle, especially if each iteration depends on the previous iteration (so no Promise.all())
I think you have to actually use a recursive function for the loop if you can't use await.

Memory is rusty and I'm too lazy to try it out

Derya Aydede

@Derya

yeah you'd have to make some nightmarish construct

thank you based async/await

Bruce Pascoe

@fatcerberus

It’s syntactic sugar as far as the behavior goes, but it being syntax makes it a lot easier to write certain constructs, like AnyhowStep says

The main advantage is you can use the value of a promise at expression-level

Whereas with .then() it’s just one step above callback hell

But other than that it's still just vanilla promise semantics under the hood, right down to the duck-typed .then

The best way to describe it is to imagine the async function is a generator, and await does something like Promise.then(x => currentGenerator.next(x)); yield;

Bruce Pascoe

@fatcerberus

Destructuring in function parameter lists still confuses the hell out of me: microsoft/TypeScript#33474
I look at the signature and it's like... okay... now exactly what am I supposed to provide at the callsite for that

I have to mentally reconstruct the destructuring in order to know what to pass to it

AnyhowStep

@AnyhowStep

Fuck that mess lol

Bruce Pascoe

@fatcerberus

microsoft/TypeScript#33479

I don't see how using the nightly helps, nightlies don't include unmerged PR features do they?

Bruce Pascoe

@fatcerberus

https://github.com/microsoft/TypeScript/issues/33475#issuecomment-532443362 - writing this up made me realize that classes should really always be nominally typed (even if there are no private properties) because of instanceof

obj instanceof B doesn't imply obj instanceof C at runtime

Guess that horse left the barn a long time ago though

Austin Cummings

@austincummings

@fatcerberus I thought the same thing when I was working on microsoft/TypeScript#32774.

Austin Cummings

@austincummings

...WRT nominal classes and instanceof

Shanon Jackson

@ShanonJackson

without providing any examples i feel like that would break interface same-name-as-class extension types

AnyhowStep

@AnyhowStep

One potential problem I might have with that narrowing is that it's possible to have A|B and then fail the A test and have it narrowed to B, even though it isn't B because it structurally matches A, just doesn't have the right prototype

@austincummings does your PR address that? =x

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