sortedLastIndexOf

INFO

This function can only be imported from es-toolkit/compat for compatibility reasons. This is because there are native JavaScript APIs that can replace it, or it hasn't been sufficiently optimized yet.

When you import this function from es-toolkit/compat , it behaves exactly the same as lodash.

Finds the index of the last occurrence of a value in a sorted array, similar to how Array#lastIndexOf works, but specifically for sorted arrays.

::: warn Ensure the array is sorted

It's important to provide a sorted array to this function because it uses a binary search to quickly find the index.

:::

Interface

export function sortedLastIndexOf(array: ArrayLike | null | undefined, value: T): number;

Parameters

• array (ArrayLike | null | undefined): A sorted array. If the array is null or undefined, it returns -1.
• value (T): The value to search for in the sorted array through comparison.

Returns

( number ): Returns the index of the last matched value, else -1.

Examples

import { sortedLastIndexOf } from 'es-toolkit/compat';

const numbers = [1, 2, 3, 4, 5];
sortedLastIndexOf(numbers, 3); // Return value: 2
sortedLastIndexOf(numbers, 6); // Return value: -1

// If the value is duplicated, it returns the last index of the value.
const duplicateNumbers = [1, 2, 2, 3, 3, 3, 4];
sortedLastIndexOf(duplicateNumbers, 3); // Return value: 5

// If the array is unsorted, it can return the wrong index.
const unSortedArray = [55, 33, 22, 11, 44];
sortedLastIndexOf(unSortedArray, 11); // Return value: -1

// -0 and 0 are treated the same
const mixedZeroArray = [-0, 0];
sortedLastIndexOf(mixedZeroArray, 0); // Return value: 1
sortedLastIndexOf(mixedZeroArray, -0); // Return value: 1

// It works with array-like objects
const arrayLike = { length: 3, 0: 10, 1: 20, 2: 20 };
sortedLastIndexOf(arrayLike, 20); // Return value: 2