How to “await” for a callback to return?

by

async/await is not magic. An async function is a function that can unwrap Promises for you, so you’ll need api.on() to return a Promise for that to work. Something like this:

function apiOn(event) {
  return new Promise(resolve => {
    api.on(event, response => resolve(response));
  });
}

Then

async function test() {
  return await apiOn( 'someEvent' ); // await is actually optional here
                                      // you'd return a Promise either way.
}

But that’s a lie too, because async functions also return Promises themselves, so you aren’t going to actually get the value out of test(), but rather, a Promise for a value, which you can use like so:

async function whatever() {
  // snip
  const response = await test();
  // use response here
  // snip
}

More Related Contents:

  1. async/await always returns promise
  2. Is async await truly non-blocking in the browser?
  3. Does an async function always need to be called with await?
  4. How to return value from an asynchronous callback function? [duplicate]
  5. Combination of async function + await + setTimeout
  6. Use async await with Array.map
  7. Correct Try…Catch Syntax Using Async/Await
  8. How can I use async/await at the top level?
  9. I know that callback function runs asynchronously, but why?
  10. How to turn this callback into a promise using async/await?
  11. How should I call 3 functions in order to execute them one after the other?
  12. How to wait for a JavaScript Promise to resolve before resuming function?
  13. How to async await in react render function?
  14. How can I take advantage of callback functions for asynchronous XMLHttpRequest?
  15. How not to forget using await everywhere in Javascript?
  16. How to use ES8 async/await with streams?
  17. Async/Await inside Array#map()
  18. How to return an Ajax result using async/await? [duplicate]
  19. Understanding async/await on NodeJS
  20. ES8 Immediately invoked async function expression
  21. Use Async/Await with Axios in React.js
  22. Waiting on multiple asynchronous calls to complete before continuing
  23. Asynchronous Script Loading Callback
  24. What are asynchronous functions in JavaScript? What is “async” and “await” in JavaScript?
  25. async/await inside arrow functions (Array#map/filter)
  26. How does javascript async/await actually work?
  27. ES2017 – Async vs. Yield
  28. Using “await” inside non-async function
  29. Load javascript async, then check DOM loaded before executing callback
  30. JS async/await – why does await need async?

Leave a Comment