Js: How To Use Generator And Yield In A Callback

I use JS generator to yield a value in a callback of setTimeout: function* sleep() { // Using yield here is OK // yield 5; setTimeout(function() { // Using yield here wi

Solution 1:

function* declaration is synchronous. You can yield a new Promise object, chain .then() to .next().value to retrieve resolved Promise value

function* sleep() {
  yield new Promise(resolve => {
    setTimeout(() => {
      resolve(5);
    }, 5000);
  })
}

// sync
const sleepTime = sleep().next().value
  .then(n => console.log(n))
  .catch(e => console.error(e));