Iterating over array elements asynchronously

Question

I'm trying to iterate asynchronously over list of array elements, but with this code:

const calculate = async ({ id, priority, database, product }) => {
    let list_of_products;
    if (priority) {
        list_of_products = await getPriorityList(database, id);
    }
    else {
        const prods = product.split(',');
        await prods.forEach((prod) => {
            list_of_products = getList(database, prod);
            console.log({ list_of_products });
        });
    }
};

I get the following console.log():

{ list_of_products : Promise { <pending> } }

And of course, an error gets thrown eventually.

What is the best practice to handle async calls when iterating? The getList() method is async as well.

You don't need to use async loop. You can just use Promise.all() https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/all — digitalniweb, Aug 26 '22 at 17:25
There are many answer [here](https://stackoverflow.com/questions/37576685/using-async-await-with-a-foreach-loop) — vee, Aug 26 '22 at 17:26
`.forEach()` should be stricken from any use with promises as it is not promise-aware. Use a regular `for` loop instead and then you can `await` the promise that `getList()` returns. — jfriend00, Aug 26 '22 at 17:36
Note that `await prods.forEach(...)` is pointless because `.forEach()` has no return value so you're doing `await undefined` which does nothing useful. `await` is ONLY useful when you are awaiting a promise. — jfriend00, Aug 26 '22 at 18:01

score 2 · Answer 1 · answered Aug 26 '22 at 17:28

do not use async await in forEach loops. await prods.forEach((prod). instead of forEach loop you can use for...of loop. checkout this: Using async/await with a forEach loop

you need to add await keyword in front of your getList(database, prod). otherwise, that async function will return a promise.

I refactored your code.

const calculate = async ({ id, priority, database, product }) => {
    let list_of_products;
    if (priority) {
        list_of_products = await getPriorityList(database, id);
    }
    else {
        const prods = product.split(',');
        for(let prod of prods) {
            list_of_products = await getList(database, prod);
            console.log({ list_of_products });
        }
    }
};

Iterating over array elements asynchronously

1 Answers1