30-seconds-of-code/snippets/runPromisesInSeries.md

title, tags, expertise, firstSeen, lastUpdated

title	tags	expertise	firstSeen	lastUpdated
Run promises in series	function,promise	intermediate	2017-12-17T17:55:51+02:00	2020-10-22T20:24:30+03:00

Runs an array of promises in series.

• Use Array.prototype.reduce() to create a promise chain, where each promise returns the next promise when resolved.

const runPromisesInSeries = ps =>
  ps.reduce((p, next) => p.then(next), Promise.resolve());

const delay = d => new Promise(r => setTimeout(r, d));
runPromisesInSeries([() => delay(1000), () => delay(2000)]);
// Executes each promise sequentially, taking a total of 3 seconds to complete