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

title, tags, expertise, firstSeen, lastUpdated

title	tags	expertise	firstSeen	lastUpdated
Unfold array	function,array	intermediate	2018-01-24T16:22:14+02:00	2020-09-15T16:28:04+03:00

Builds an array, using an iterator function and an initial seed value.

• Use a while loop and Array.prototype.push() to call the function repeatedly until it returns false.
• The iterator function accepts one argument (seed) and must always return an array with two elements ([value, nextSeed]) or false to terminate.

const unfold = (fn, seed) => {
  let result = [],
    val = [null, seed];
  while ((val = fn(val[1]))) result.push(val[0]);
  return result;
};

var f = n => (n > 50 ? false : [-n, n + 10]);
unfold(f, 10); // [-10, -20, -30, -40, -50]