reduceRight (Lodash Compatibility)

Use Array.prototype.reduceRight or Object.values with reduceRight

This reduceRight function operates slowly due to complex type handling and support for various input formats.

Instead, use the faster and more modern Array.prototype.reduceRight method, or for objects, use reduceRight together with Object.values.

Reduces an array or object to a single value by iterating from right to left.

const result = reduceRight(collection, iteratee, initialValue);

Reference

reduceRight(collection, iteratee, initialValue)

Iterates through all elements of an array or object from right to left to calculate an accumulated value. If an initial value is provided, it starts with that value; otherwise, it starts with the last element.

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

// Concatenate array to string (from right)
const letters = ['a', 'b', 'c', 'd'];
const result = reduceRight(letters, (acc, value) => acc + value, '');
console.log(result); // 'dcba'

// Multiply object values (reverse of key order)
const numbers = { x: 2, y: 3, z: 4 };
const product = reduceRight(numbers, (acc, value) => acc * value, 1);
console.log(product); // 24 (1 * 4 * 3 * 2)

If no initial value is provided, the last element becomes the initial value and iteration starts from the second to last element.

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

const numbers = [1, 2, 3, 4];
const sum = reduceRight(numbers, (acc, value) => acc + value);
console.log(sum); // 10 (4 + 3 + 2 + 1)

// Empty array returns undefined
const empty = [];
const result = reduceRight(empty, (acc, value) => acc + value);
console.log(result); // undefined

Parameters

• collection (T[] | ArrayLike<T> | Record<string, T> | null | undefined): The array or object to iterate over.
• iteratee ((accumulator: any, value: any, index: PropertyKey, collection: any) => any): The function to call for each element. It receives the accumulated value, current value, index/key, and the original array/object.
• initialValue (any, optional): The initial value for the accumulator. If not provided, the last element becomes the initial value.

Returns

(any): Returns the final accumulated value after processing all elements.