What is an async function?

async function foo() {
  ...
}

Answer

An async function is a function that allows you to pause the function's execution while it waits for (awaits) a promise to resolve. It's an abstraction on top of the Promise API that makes asynchronous operations look like they're synchronous.

async functions automatically return a Promise object. Whatever you return from the async function will be the promise's resolution. If instead you throw from the body of an async function, that will be how your async function rejects the promise it returns.

Most importantly, async functions are able to use the await keyword in their function body, which pauses the function until the operation after the await completes, and allows it to return that operation's result to a variable synchronously.

// Normal promises in regular function:
function foo() {
  promiseCall()
    .then(result => {
      // do something with the result
    })
}

// async functions
async function foo() {
  const result = await promiseCall()
  // do something with the result
}

Good to hear

• async functions are just syntactic sugar on top of Promises.

• They make asynchronous operations look like synchronous operations in your function.

• They implicitly return a promise which resolves to whatever your async function returns, and reject to whatever your async function throws.

Additional links

• MDN Docs - async function
• MDN Docs - await