JavaScript async/await implemented in V8

Post by [deleted] » Tue, May 17, 2016, 6:04 AM UTC

calebegg wrote: post #68

dvlsg wrote: post #28

Earlier quoted context omitted.

Just to be picky, but I believe you would be better off with this: async function main () { try { const jsons = await Promise.all([ fetch('https://api.github.com/orgs/facebook'), fetch('https://api.github.com/orgs/facebook') ]).map(promise => promise.then(res => res.json())); } catch (err) { console.log(err) } } This way, if one response was much quicker than the other, you could begin sending it through the `res.jso…

Nit -- you want: async function main () { try { const jsons = await Promise.all([ fetch('https://api.github.com/orgs/facebook'), fetch('https://api.github.com/orgs/facebook') ].map(promise => promise.then(res => res.json()))); } catch (err) { console.log(err) } } As written you get "Promise.all(...).map is not a function"

Post by MichaelGG » Tue, May 17, 2016, 6:11 AM UTC

Lx1oG-AWb6h_ZG0 wrote: post #84

bigtones wrote: post #77

Thank you to Microsoft and Anders Hejlsberg for inventing Async/Await (and to F# for the original inspiration) https://en.wikipedia.org/wiki/Futures_and_promises

async/await as we know it actually came from Midori's C# dialect, which indeed was inspired from F#: http://joeduffyblog.com/2015/11/19/asynchronous-everything/ (Although, just to be pedantic, the concept of futures is way older than F#. Alice's syntax, for example, is pretty close)

Post by dvlsg » Tue, May 17, 2016, 6:17 AM UTC

calebegg wrote: post #68

dvlsg wrote: post #28

Earlier quoted context omitted.

Just to be picky, but I believe you would be better off with this: async function main () { try { const jsons = await Promise.all([ fetch('https://api.github.com/orgs/facebook'), fetch('https://api.github.com/orgs/facebook') ]).map(promise => promise.then(res => res.json())); } catch (err) { console.log(err) } } This way, if one response was much quicker than the other, you could begin sending it through the `res.jso…

Nit -- you want: async function main () { try { const jsons = await Promise.all([ fetch('https://api.github.com/orgs/facebook'), fetch('https://api.github.com/orgs/facebook') ].map(promise => promise.then(res => res.json()))); } catch (err) { console.log(err) } } As written you get "Promise.all(...).map is not a function"

Post by dvlsg » Tue, May 17, 2016, 6:19 AM UTC

jdgiese wrote: post #66

dvlsg wrote: post #50

Earlier quoted context omitted.

Yes. They will be sent into map immediately, and Promise.all() will return a Promise which will settle when the mapped array is all settled (or one errors, but that's not really relevant to the question). We're really just awaiting the promise returned from Promise.all(), but mapping the original fetches into a "new" set of promises.

I'm sorry, but I don't see why/how they would be sent to `map` immediately, given where the parenthesis are in the above code snippet. `Promise.prototype.map` isn't a builtin function is it? If the `map` call was inside the invocation of `Promise.all` then I could see it, but perhaps I am missing something.

Post by dvlsg » Tue, May 17, 2016, 6:24 AM UTC

jeswin wrote: post #51

avodonosov wrote: post #30

what's the point of explicitly declaring functions "async", and then explicitly saying "await". IMHO all this could be done automatically by language.

Because you don't always have to await a function, and it isn't always possible for the runtime or language to decide whether to "await" or not. /* The following code may or may not use an await. Not await-ing would be better user experience. */ async function sendEmails(id) { ... } async function signUp(userData) { const user = await db.saveUser(userData); sendEmails(user.id); //