sortedIndexBy (Lodash compatibility)

Implement binary search and transformation function directly

This sortedIndexBy function operates slowly due to complex iteratee handling and type conversion.

Instead, implement faster, more modern binary search and transformation functions directly.

Finds the lowest index at which a value should be inserted into a sorted array after applying a transformation function.

const index = sortedIndexBy(array, value, iteratee);

Reference

sortedIndexBy(array, value, iteratee)

Use sortedIndexBy to find the insertion position of a value in a sorted array after applying a transformation function. It applies the transformation function to each element and the value to compare.

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

// Find insertion position in object array sorted by property
const objects = [{ x: 4 }, { x: 5 }];
sortedIndexBy(objects, { x: 4 }, 'x');
// Returns 0

// Transform using function
const numbers = [10, 20, 30];
sortedIndexBy(numbers, 25, n => n);
// Returns 2

// Transform with property-value array
const users = [{ name: 'alice' }, { name: 'bob' }];
sortedIndexBy(users, { name: 'bob' }, ['name', 'bob']);
// Returns 1 (equivalent to inserting true into [false, true])

For null or undefined arrays, returns 0.

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

sortedIndexBy(null, { x: 1 }, 'x'); // 0
sortedIndexBy(undefined, { x: 1 }, 'x'); // 0

Parameters

• array (ArrayLike<T> | null | undefined): The sorted array. Using an unsorted array can produce incorrect results.
• value (T): The value to insert.
• iteratee (optional): The transformation function, property name, or property-value array to apply to each element and value.

Returns

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