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for-await-of vs Promise.all

for-await-of

 When there are multiple async functions, we can use for-await-of to resolve the problem.

It's especially useful when working with a series of asynchronous operations that are dependent on the previous operation.


for example:

async function processArray(array) { for await (let item of array) { await doSomethingAsync(item); } }

In this example, doSomethingAsync(item) is not started until the previous call to doSomethingAsync has completed. This is sequential execution.


Promise.all()

Promise.all() is a method that returns a single Promise that resolves when all of the promises passed as an iterable have resolved or when the iterable contains no promises. It rejects with the reason of the first promise that rejects.

In this example, doSomethingAsync(item) is started for all items in the array at roughly the same time, and Promise.all() waits for all of them to complete. This is parallel execution.


Difference

The key difference between for-await-of and Promise.all() is the way they handle concurrency:

  • for-await-of processes one item at a time, waiting for each promise to resolve before moving on to the next one. It's useful when the order of execution matters, or when each asynchronous operation depends on the result of the previous one.

  • Promise.all() processes all items at the same time (in parallel). It's useful when you want to run multiple independent promises concurrently and wait for all of them to complete.



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