CODEWITHSUNDEEP
node.jsloopsasync-awaites6-promise
user19471776
user19471776

Reputation:

How does error handling work for async map inside an async function?

I have successfully created a function that creates folders according to a directory.

However, when I have tried to convert the for of into a map() method using Promise.all(), the error was not handled the same.

import { readdir, mkdir } from 'fs/promises';

const copyUsingFor = async (target) => {
    try {
        const dir = await readdir(`./test`, { withFileTypes: true });
        for (const item of dir) {
            if (item.isDirectory()) {
                try {
                    await mkdir(`./${target}`);
                }
                catch (err) {
                    throw err;
                }
            }
        }
    }
    catch (err) {
        console.log(`desired err handling`);
        throw err;
    }
}

const copyUsingMap = async (target) => {
    try {
        const dir = await readdir(`./test`, { withFileTypes: true });
        Promise.all(
            dir.map(async item => {
                if (item.isDirectory()) {
                    try {
                        await mkdir(`./${target}`);
                    }
                    catch (err) {
                        throw err;
                    }
                }
            })
        )
    }
    catch (err) {
        throw err;
    }
}

copyUsingFor(`../`).catch(err => console.log(`An error occurred: ${err}`)) // <- Works.
copyUsingMap(`../`).catch(err => console.log(`An error occurred: ${err}`)) // <- Gives "triggerUncaughtException".

I am guessing it is because I have an async inside another, but could not figure out why it does not works the same.

Thanks!

Upvotes: 1

Views: 1084

Answers (1)

CherryDT
CherryDT

Reputation: 29012

You are missing the await in front of Promise.all, that's all. Because of this, what happens inside the Promise.all is detached from the rest of your program flow.

Side note: catch (err) { throw err } is a no-op. You can get rid of the whole try/catch if you don't do anything other than rethrowing the error in it. It feels a bit like wrapping stuff in a call to a function x => x.

Upvotes: 1

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