JuniorTheoryCommon

What does the program print (lines separated by spaces)?

JavaScript

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

Promise.all([wait(30, "a"), wait(10, "b")])
    .then((values) => console.log(values.join(" ")));
console.log("start");

start a b

Expecting start b a: Promise.all gives the values in the order of the input array, not in the order the promises were fulfilled.
Expecting start b: Promise.all waits for every promise in the array, not only the first one that is ready.

How long does the program run before it prints the array, and why?
What happens if wait(10, "b") is replaced with a rejected promise?

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JuniorTheoryCommon

What does the program print (lines separated by spaces)?

JavaScript

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

Promise.all([wait(30, "a"), wait(10, "b")])
    .then((values) => console.log(values.join(" ")));
console.log("start");

start a b

Expecting start b a: Promise.all gives the values in the order of the input array, not in the order the promises were fulfilled.
Expecting start b: Promise.all waits for every promise in the array, not only the first one that is ready.

How long does the program run before it prints the array, and why?
What happens if wait(10, "b") is replaced with a rejected promise?

Back to questions Open topic in roadmap →Answer it yourself — Quiz