How to add delay to promise inside then [duplicate]

Question

Return a promise from the then handler that waits:

.then(() => new Promise(resolve => setTimeout(resolve, 1000)))

If you want to “pass through” the value of the promise, then

.then(x => new Promise(resolve => setTimeout(() => resolve(x), 1000)))

To avoid this boilerplate everywhere, write a utility function:

function sleeper(ms) {
  return function(x) {
    return new Promise(resolve => setTimeout(() => resolve(x), ms));
  };
}

then use it as in

.then(sleeper(1000)).then(...)