Using async/await with a forEach loop

Instead of Promise.all in conjunction with Array.prototype.map (which does not guarantee the order in which the Promises are resolved), I use Array.prototype.reduce, starting with a resolved Promise:

async function printFiles () {

  const files = await getFilePaths();



  await files.reduce(async (promise, file) => {

    // This line will wait for the last async function to finish.

    // The first iteration uses an already resolved Promise

    // so, it will immediately continue.

    await promise;

    const contents = await fs.readFile(file, 'utf8');

    console.log(contents);

  }, Promise.resolve());

}

3 years ago

Sure the code does work, but I'm pretty sure it doesn't do what you expect it to do. It just fires off multiple asynchronous calls, but the printFiles function does immediately return after that.
Reading in sequence
If you want to read the files in sequence, you cannot use forEach indeed. Just use a modern for … of loop instead, in which await will work as expected:

async function printFiles () {

  const files = await getFilePaths();



  for (const file of files) {

    const contents = await fs.readFile(file, 'utf8');

    console.log(contents);

  }

}

Reading in parallel
If you want to read the files in parallel, you cannot use forEach indeed. Each of the async callback function calls does return a promise, but you're throwing them away instead of awaiting them. Just use map instead, and you can await the array of promises that you'll get with Promise.all:

async function printFiles () {

  const files = await getFilePaths();



  await Promise.all(files.map(async (file) => {

    const contents = await fs.readFile(file, 'utf8')

    console.log(contents)

  }));

}

3 years ago

Use the below code

async function printFiles () {

  const files = await getFilePaths()



  for await (const contents of files.map(file => fs.readFile(file, 'utf8'))) {

    console.log(contents)

  }

}

3 years ago