sortedLastIndexOf (Lodash compatibility)

Implement binary search directly

This sortedLastIndexOf function operates slowly due to complex binary search handling and type validation.

Instead, implement faster, more modern binary search directly or use Array.prototype.lastIndexOf().

Finds the index where a value last appears in a sorted array.

const index = sortedLastIndexOf(array, value);

Reference

sortedLastIndexOf(array, value)

Use sortedLastIndexOf to find the index where a specific value last appears in a sorted array. It uses binary search to find the value quickly.

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

// Find value in number array
sortedLastIndexOf([1, 2, 3, 4, 5], 3);
// Returns 2

// When value doesn't exist
sortedLastIndexOf([1, 2, 3, 4, 5], 6);
// Returns -1

// When duplicate values exist, returns the last index
sortedLastIndexOf([1, 2, 2, 3, 3, 3, 4], 3);
// Returns 5 (position of the last 3)

// 0 and -0 are treated as equal
sortedLastIndexOf([-0, 0], 0);
// Returns 1

Empty arrays, null, or undefined return -1.

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

sortedLastIndexOf([], 1); // -1
sortedLastIndexOf(null, 1); // -1
sortedLastIndexOf(undefined, 1); // -1

Parameters

• array (ArrayLike<T> | null | undefined): The sorted array. Using an unsorted array can produce incorrect results.
• value (T): The value to find.

Returns

(number): Returns the index where the value last appears. If the value doesn't exist, returns -1.