For AI agents: the complete documentation index is available at /llms.txt, the full documentation bundle is available at /llms-full.txt, and this page is available as Markdown at /reference/fp/findLastIndex.md.
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    findLastIndex (Functional Programming) es-toolkit

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

    const result = pipe(array, findLastIndex(predicate));
    Info

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

    Usage

    findLastIndex searches the piped array from the end and returns the index of the first value for which predicate returns true. If no value matches, it returns -1.

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

pipe(
  [1, 2, 3, 4],
  findLastIndex(value => value % 2 === 0)
); // => 3

    Parameters

    predicate(value: T, index: number) => booleanrequired

    The function that tests each value.

    Returns

    A function that maps a readonly T[] to the last matching index, or -1.

    (array: readonly T[]) => number
    Source: es-toolkit

    Re-exported verbatim from es-toolkit. Implementation, edge cases, and performance behavior are owned upstream. This page mirrors the documentation at the pinned version; the linked source is authoritative.