iterate (for Iterators)

Creates an infinite lazy iterator by repeatedly applying a function to a seed value.

const sequence = iterate(seed, getNext);

Usage

iterate(seed, getNext)

Use iterate to generate a sequence where each value is derived from the previous one — powers, running dates, retry delays, and so on. The sequence starts with seed and continues with getNext(seed), getNext(getNext(seed)), and so on. Nothing is computed before the iterator is consumed, and getNext only runs as many times as values are pulled.

Because the iterator is infinite, it must be bounded by a short-circuiting helper such as the native take or takeWhile before being consumed.

import { iterate } from 'es-toolkit/iterator';
// Returns: [1, 2, 4, 8, 16]
// Exponential backoff delays below one minute.
import { takeWhile } from 'es-toolkit/iterator';

// Powers of two, bounded by take.
iterate(1, x => x * 2)
  .take(5)
  .toArray();

takeWhile(
  iterate(100, x => x * 2),
  x => x < 60000
).toArray();
// Returns: [100, 200, 400, ..., 51200]

Parameters

• seed (T): The first value of the sequence.
• getNext ((value: T) => T): Computes the next value from the current one.

Returns

(IteratorObject<T, undefined>): An infinite lazy iterator over the generated sequence. It carries every native iterator helper (map, take, toArray, ...) for further chaining.