sortedLastIndex (Lodash compatibility)

Implement binary search directly

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

Instead, implement faster, more modern binary search directly.

Finds the highest index at which a value should be inserted into a sorted array.

const index = sortedLastIndex(array, value);

Reference

sortedLastIndex(array, value)

Use sortedLastIndex to find the highest position to insert a value in a sorted array. When duplicate values exist, it returns the index after the last position.

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

// Find last insertion position in array with duplicate values
sortedLastIndex([4, 5, 5, 5, 6], 5);
// Returns 4 (position after the last 5)

// Find insertion position for new value
sortedLastIndex([10, 20, 30], 25);
// Returns 2 (25 is positioned before 30)

// When value doesn't exist
sortedLastIndex([1, 2, 3], 0);
// Returns 0 (positioned at the front)

For null or undefined arrays, returns 0.

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

sortedLastIndex(null, 1); // 0
sortedLastIndex(undefined, 1); // 0

Parameters

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

Returns

(number): Returns the highest index to insert the value. If the array is null or undefined, returns 0.