Use this tag for questions about features finalized in ECMAScript 2017. Do *not* use this tag if the code in question merely *uses* one of the features, *unless* the feature is cause of the problem.
Proposals finalized in 2017 include:
Questions tagged [ecmascript-2017]
387 questions
2999
votes
33 answers
Using async/await with a forEach loop
Are there any issues with using async/await in a forEach loop? I'm trying to loop through an array of files and await on the contents of each file.
import fs from 'fs-promise'
async function printFiles () {
const files = await getFilePaths() //…
Saad
- 49,729
- 21
- 73
- 112
681
votes
19 answers
Combination of async function + await + setTimeout
I am trying to use the new async features and I hope solving my problem will help others in the future. This is my code which is working:
async function asyncGenerator() {
// other code
while (goOn) {
// other code
var fileList…
JShinigami
- 7,317
- 3
- 14
- 22
514
votes
9 answers
Use async await with Array.map
Given the following code:
var arr = [1,2,3,4,5];
var results: number[] = await arr.map(async (item): Promise => {
await callAsynchronousOperation(item);
return item + 1;
});
which produces the following error:
TS2322:…
Alon
- 10,381
- 23
- 88
- 152
468
votes
15 answers
How can I use async/await at the top level?
I have been going over async/await and after going over several articles, I decided to test things myself. However, I can't seem to wrap my head around why this does not work:
async function main() {
var value = await Promise.resolve('Hey…
Felipe
- 10,606
- 5
- 40
- 57
464
votes
8 answers
How to reject in async/await syntax?
How can I reject a promise that returned by an async/await function?
e.g. Originally:
foo(id: string): Promise {
return new Promise((resolve, reject) => {
someAsyncPromise().then((value)=>resolve(200)).catch((err)=>reject(400))
…
Phoenix
- 4,773
- 2
- 10
- 6
227
votes
10 answers
try/catch blocks with async/await
I'm digging into the node 7 async/await feature and keep stumbling across code like this
function getQuote() {
let quote = "Lorem ipsum dolor sit amet, consectetur adipiscing elit laborum.";
return quote;
}
async function main() {
try {
…
Patrick
- 7,903
- 11
- 52
- 87
164
votes
6 answers
How to "await" for a callback to return?
When using a simple callback such as in the example below:
test() {
api.on( 'someEvent', function( response ) {
return response;
});
}
How can the function be changed to use async / await? Specifically, assuming 'someEvent' is guaranteed…
sean2078
- 5,131
- 6
- 32
- 32
133
votes
6 answers
Correct Try...Catch Syntax Using Async/Await
I like the flatness of the new Async/Await feature available in Typescript, etc. However, I'm not sure I like the fact that I have to declare the variable I'm awaiting on the outside of a try...catch block in order to use it later. Like so:
let…
freedomflyer
- 2,431
- 3
- 26
- 38
125
votes
7 answers
How to use ES8 async/await with streams?
In https://stackoverflow.com/a/18658613/779159 is an example of how to calculate the md5 of a file using the built-in crypto library and streams.
var fs = require('fs');
var crypto = require('crypto');
// the file you want to get the hash
var…
user779159
- 9,034
- 14
- 59
- 89
103
votes
3 answers
Property 'entries' does not exist on type 'ObjectConstructor'
I'm working on an ng2 implementation. I'm using the following function call to convert an object to an array:
var authors = Object.entries(responseObject.Authors);
This is a standard js function. However, the ts compiler returns the following…
user8334943
- 1,467
- 3
- 11
- 21
100
votes
3 answers
Does awaiting a non-Promise have any detectable effect?
One can await a non-Promise and that's good so.
All these expressions are valid and cause no error:
await 5
await 'A'
await {}
await null
await undefined
Is there any detectable effect of awaiting a non-Promise? Is there any difference in behavior…
ttulka
- 10,309
- 7
- 41
- 52
88
votes
6 answers
async/await inside arrow functions (Array#map/filter)
I'm getting compile time error in this code:
const someFunction = async (myArray) => {
return myArray.map(myValue => {
return {
id: "my_id",
myValue: await service.getByValue(myValue);
}
});
};
Error…
WelcomeTo
- 19,843
- 53
- 170
- 286
77
votes
5 answers
how to async/await redux-thunk actions?
action.js
export function getLoginStatus() {
return async(dispatch) => {
let token = await getOAuthToken();
let success = await verifyToken(token);
if (success == true) {
dispatch(loginStatus(success));
} else {
…
nabeel
- 1,181
- 2
- 10
- 24
76
votes
4 answers
(ES6) class (ES2017) async / await getter
Is it or will it be possible to have an ES6 class getter
return a value from an ES2017 await / async function.
class Foo {
async get bar() {
var result = await someAsyncOperation();
return result;
}
}
function…
Enki
- 1,565
- 2
- 13
- 20
74
votes
6 answers
async function - await not waiting for promise
I'm trying to learn async-await. In this code -
const myFun = () => {
let state = false;
setTimeout(() => {state = true}, 2000);
return new Promise((resolve, reject) => {
setTimeout(() => {
if(state) {
…
hg_git
- 2,884
- 6
- 24
- 43