Error handling in a Promise.all like flow in async/await syntax

Question

I have some issues to handle multiple rejections in "parallel". How to handle rejection in a async function when we "await in parallel".
Here an example :

function in_2_sec(number) {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            reject('Error ' + number);
        }, 2000);
    }) 
}

async function f1() {
    try {
        let a = in_2_sec(3);
        let b = in_2_sec(30);
        return await a + await b; // awaiting in "parallel"
    } catch(err) {
        console.log('Error', err);
        return false;
    }
}

async function f2() {
    try {
        let a = await Promise.all([in_2_sec(3), in_2_sec(30)]);
        return a[0] + a[1];
    } catch(err) {
        console.log('Error', err);
        return false;
    }
}

// f1().then(console.log) // UnhandledPromiseRejectionWarning
// f2().then(console.log) // Nice

f1() create a UnhandledPromiseRejectionWarning in node, because the second rejection (b) is not handled.
f2() works perfectly, Promise.all() do the trick, but how to make a f2() with only async/await syntax, without Promise.all() ?

Answer 1

f2() works perfectly, Promise.all() do the trick, but how to make a f2() with only async/await syntax, without Promise.all()?

Not at all. Use Promise.all! This is what it was made for. Don't think of async/await of replacing promises - you still are using them, it's only syntactic sugar for then calls. There is no syntactic replacement for Promise.all.

Of course it's also possible to re-implement the behaviour of Promise.all yourself (relying on the Promise constructor and .then primitives), but you really don't want to do that (there are too many pitfalls).