在异步函数内的回调中调用 await

Question

Here is some code (it's an over-simplified example, I know it is dumb):

function sleep(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
}

async function test() {
    [1, 2, 3].map(() => {
        console.log('test');
        await sleep(1000);
    });
}
test();

The objective is to:

1. display test then wait one second
2. then display test then wait one second
3. then display test then wait one second

But running this code results in a failure:

await is a reserved word

I know I can do fix it by using a for loop:

async function test() {
    for(let i = 0; i < 3; i++) {
        console.log('test');
        await sleep(1000);
    }
}

But is there a way to do it in a more "functional" way. I mean, can I avoid the for loop and await inside a map?

Answer 1

const result = await [1, 2, 3].reduce(async function(prom, v){   
    const result= await prom;
    await sleep(1000);
    result.push(v);
    return result;
 }, Promise.resolve([]));

You could reduce to create a promise chain. However in your simplyfied case:

(a=b=>(b==2||(console.log("test"),setTimeout(a,1000,b+1))))(0);

Answer 2

If a library like bluebird is an option then you could write:

'use strict'
const Promise = require('bluebird')


async function test() {
  return Promise.mapSeries([1, 2, 3], async (idx) => {
    console.log('test: ' + idx);
    await Promise.delay(1000)
  });
}
test();