JavaScript Concurrency: Async/await in Arrow Functions

• So far we've only seen async/await in regular JavaScript functions, but it works in arrow functions too. The async comes before the parameter list, and await can be used in the body as normal.

• >

  const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));
  sleep(500).then(() => 'it worked');

  Async Result:

  Asynchronous ResultThis result will wait up to 3000ms for a response from the code before returning.

  {fulfilled: 'it worked'}

• Here's that same function with async/await.

• >

  const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));
  const delayed1 = async () => {
    await sleep(500);
    return 'it worked';
  };
  delayed1();

  Async Result:

  Asynchronous ResultThis result will wait up to 3000ms for a response from the code before returning.

  {fulfilled: 'it worked'}

• Fortunately, there's nothing else that's special about asynchronous arrow functions. They work just like regular functions!

• Here's a code problem:

  We rewrote sleep below as an arrow function using await. It's not an async function, so the await causes an error. Change the function to make it async.

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  const sleep = async (ms) => {

  await new Promise(resolve => setTimeout(resolve, ms));

  };

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  const startTime = new Date().getTime();

  sleep(500).then(() => {

  const now = new Date().getTime();

  const elapsed = now - startTime;

  return elapsed >= 100;

  });

  Async Result:

  Asynchronous ResultThis result will wait up to 3000ms for a response from the code before returning.

  Goal:

  {fulfilled: true}

  Yours:

  {fulfilled: true}

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