findIndex (Functional Programming)

Creates a function that returns the index of the first value that passes a test. Use it with pipe.

typescript

const result = pipe(array, findIndex(predicate));

::: info

This helper is specific to es-toolkit/fp. Use it when you want this operation as part of a pipe pipeline.

:::

Usage

findIndex returns the index of the first value in the piped array for which predicate returns true. If no value matches, it returns -1.

typescript

import { findIndex, pipe } from 'es-toolkit/fp';

pipe(
  [1, 2, 3, 4],
  findIndex(value => value > 2)
); // => 2

predicate ((value: T, index: number) => boolean): The function that tests each value.

((array: readonly T[]) => number): A function that maps a readonly T[] to the first matching index, or -1.