JavaScript (ES2026) reference · Array Methods

JavaScript Array reduceRight() Method

Like reduce(), but processes the array from the last element to the first.

JavaScript (ES2026) Since ES5

Syntax

array.reduceRight(callbackFn, initialValue)

Parameters

Parameter	Description
`callbackFn`	Called with `(accumulator, element, index, array)`.
`initialValue` optional	The starting accumulator.

Return value

The final accumulator value.

Examples

Right to leftTry it yourself

console.log(["a", "b", "c"].reduceRight((acc, x) => acc + x, ""));

Output

cba

Compose functionsTry it yourself

const compose = (...fns) => (x) => fns.reduceRight((v, f) => f(v), x);
const inc = (n) => n + 1, double = (n) => n * 2;
console.log(compose(inc, double)(5)); // inc(double(5))