2021-11-08
2621
#vanilla javascript
Fernando Doglio
4429
Nov 8, 2021 â‹… 9 min read

JavaScript Promises: race, all, allSettled, and then

Fernando Doglio Technical Manager at Globant. Author of books and maker of software things. Find me online at fdoglio.com.

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3 Replies to "JavaScript Promises: race, all, allSettled, and then"

  1. Mozilla’s web documentation at https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/all has an good workaround for the problem of rejection stopping Promise.all(). I have been using it without any issues so far:

    var p1 = new Promise((resolve, reject) => {
    setTimeout(() => resolve(‘p1_delayed_resolution’), 1000);
    });

    var p2 = new Promise((resolve, reject) => {
    reject(new Error(‘p2_immediate_rejection’));
    });

    Promise.all([
    p1.catch(error => { return error }),
    p2.catch(error => { return error }),
    ]).then(values => {
    console.log(values[0]) // “p1_delayed_resolution”
    console.log(values[1]) // “Error: p2_immediate_rejection”
    })

  2. Nice article, but one thing should be noted. You say:

    “By definition,Promise.all will run all your promises until one of the following conditions are met:”

    It’s not true. Promise.all doesn’t run anything. Promises are ALWAYS fired immediately, always. There are no methods to explicitly control Promise’s execution. Promise.all just listens their execution, but doesn’t do anything else.

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