Serial Execution of Promise

Question

I would like to execute a function with a parameter looping from an array of values. Every execution must waits the previous to be completed. The example code below should print:

Done: 1
Done: 2
Done: 3
Done: 4
Done: 5

Thanks!

p.

'use strict';

function f1(value) {
    return new Promise((resolve, reject) => {
        setTimeout(function() {
            console.log('Done: ' + value);
            resolve(true)
        }, Math.random() * 2000 + 1000);
    });
}

const vs = [0,1,2,3,4,5];

vs.reduce((start, next) => {
    return f1(next)
})

I made this using angularjs promises however exactly the same can be done with native. https://gist.github.com/ste2425/608b74d20504d526d2c08dd8fa76f675 — ste2425, Jul 08 '16 at 16:25

score 4 · Accepted Answer · edited May 23 '17 at 11:52

4

If you want just ES6, try this:

'use strict';

function f1(value) {
    return new Promise((resolve, reject) => {
        setTimeout(function() {
            console.log('Done: ' + value);
            resolve(true)
        }, Math.random() * 2000 + 1000);
    });
}

const vs = [0,1,2,3,4,5];

let promiseChain = vs.reduce((start, next) => {
    return start.then(() => f1(next));
}, Promise.resolve());

promiseChain.then(() => console.log('Done!'));

If you're interested in getting the values out of the resolutions, you can try this as well.

edited May 23 '17 at 11:52

Community

1
1

answered Jul 08 '16 at 16:11

dvlsg

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It's what I'd try to do! Thanks – goliardico Jul 08 '16 at 17:10
1

Or just `vs.reduce((p, v) => p.then(() => f1(v)), Promise.resolve())`. – jib Jul 08 '16 at 22:32
Right, same thing. I just opted for multiple lines and re-using the variable names from the question to (hopefully) improve readability. – dvlsg Jul 08 '16 at 22:59

Serial Execution of Promise

1 Answers1