How to await async functions in specific sequence using typescript

Published on August 04, 2019

I was posting messages to a slack webhook recently and I wanted to post a list of messages in the correct order. I had to await each one before calling the next. I tried a few different methods but only one worked the way I expected it to.

// 1.  array.forEach - Doesn't work!

listofMessages.forEach(async (x) => await postMessage(x))

// this doesn't work becuase the foreach creates a new function
// per item and you essentially ignore or throw away the returned Promise.

// 2. foreach (x in y) - Doesn't work and I learned something new!

for (let message in messages) {
  await postMessage(x)

// this doesn't work because it's a completely incorrect usage of!
// In JS the construct is designed to be used to iterate over and objects properties
// and it's known to have issues when iterating over an array

// 3. foreach (x of y) - Works! The correct way.

for (let message of messages) {
  await postMessage(x)

// this works as expected. Each call is awaited before the loop continues.
Darragh ORiordan

Hi! I'm Darragh ORiordan.

I live and work in Sydney, Australia enjoying the mountains and the ocean.

I build and support happy teams that create high quality software for the web.

Contact me on Twitter!

Sign up for the newsletter

Get new writings, curated tech articles and coding tips!

Read the Privacy Policy.