How do async/await and Promise.all differ when working with asynchronous operations in JavaScript?

async/await and Promise.all are different mechanisms for handling asynchronous operations in JavaScript, which are often used together but solve different tasks.

• async/await is syntactic sugar over promises, allowing you to write asynchronous code in a synchronous style. It enables waiting for a promise to resolve before continuing.

• Promise.all takes an array of promises and returns a new promise that:

  • resolves when all promises in the array are successfully completed,
  • rejects if at least one promise is rejected.

Example of using them together:

async function fetchData() {
  const results = await Promise.all([
    fetch(url1),
    fetch(url2),
    fetch(url3)
  ]);
  // results is an array of responses
}

Here, Promise.all runs all requests in parallel, and await waits for all of them to finish.

If you use only await sequentially:

async function fetchDataSequential() {
  const res1 = await fetch(url1);
  const res2 = await fetch(url2);
  const res3 = await fetch(url3);
}

the requests will be executed sequentially, which is slower.

In summary:

• async/await simplifies reading asynchronous code.
• Promise.all allows running multiple asynchronous operations in parallel and waiting for all of them.