Make an async function take at least X amount of time

waitAtLeast.js

/**
 * make an async function take at least X amount of time
 * @param limit - in ms
 * @param fn - returns promise
 * @returns {Promise.<T>}
 */
function waitAtLeast(limit, fn) {
	let start = Date.now();
	let end = start + limit;

	return fn().then(result => {
		let now = Date.now();
		if((now - start) > end) {
			return result;
		}
		else {
			return sleep(end - now).then(() => result);
		}
	});
}

// promisified setTimeout
function sleep(ms) {
  return new Promise((res, rej) => {
    setTimeout(res, ms);
  });
}