async and await

async/await allows us to make Promises synchronous with other code.

async is a keyword that is used in front of a function definition to make the function return a Promise and allow it to use the await keyword - once all the lines of code are executed in the async function, it will change the returned Promise to be resolved

async/await are keywords that we need to use together and should not be used without each other.

await is used in front of a Promise in an async function. - It should not be used in front of a line of code that isn’t a Promise - evaluates to the result of the awaited Promise (or what the Promise’s resolve value is)

const myPromise = new Promise((resolve, reject) => {
  setTimeout(() => resolve(3), 1000)
});


async function asyncFunc() {
  console.log('before await');
  const res = await myPromise; // res = 3
  console.log('after await');
}

asyncFunc() // returns Promise pending until all lines of code have been executed
// before await
// 3
// after await (waits for myPromise to resolve)

Learning Objectives

1. Use async/await with promise-based functions to write asynchronous code that behaves synchronously.