In JavaScript, we can’t directly use async/await keywords with a forEach loop because the forEach
loop doesn’t work with asynchronous functions. It doesn’t wait for asynchronous operations to complete before moving to the next iteration.
async
/await
feature in a forEach
loopIn JavaScript, async/await
is a powerful feature for handling asynchronous operations in a more synchronous-looking way. However, when it comes to using async/await
within a forEach
loop, there’s a common pitfall that developers often encounter.
Consider the following code:
const items = [1, 2, 3, 4, 5];function someAsyncFunction(it){sleep(100)return it;}items.forEach(async (item) => {let result;try {result = await someAsyncFunction(item);} catch (error) {result = undefined;}console.log(result);});console.log('Loop finished');
In this code, we have an array (items
) and we want to perform some asynchronous operation (someAsyncFunction
) on each item in the array and log the result. However, the output might surprise us when we run this code.
Note: The
someAsyncFunction
function is just a dummy method to show the functionality of waiting call/API call.
The forEach
loop doesn’t wait for the async
function to complete before moving on to the next iteration. As a result, it logs Loop finished
before any of the asynchronous operations are completed, and the undefined
values are logged because the promises returned by the async
functions haven’t been resolved yet.
However, we can do a workaround to make it possible. While forEach
itself doesn't support the async/await
feature, we can still use async/await
within a forEach
loop by defining and immediately invoking an asynchronous function within the map() function as implemented in the code below.
async function dummyArray(array) {await (array.map(async (item) => {// Perform some asynchronous operation using awaitsetTimeout(()=>{console.log(`${item} processed`);},5000)}));}// Usage example:const myArray = [1, 2, 3, 4];dummyArray(myArray);
Lines 2–6: We create an async (item)
) within the map()
function, which allows us to use await
inside the loop. The setTimeout
function waits for 5000
milliseconds here and acts like an API call that can take some time to respond to mimic the functionality of the async
/await
feature.
This approach allows us to use async
/await
feature with a forEach
loop-like structure, providing the expected behavior of processing each item in the array asynchronously and in order.
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