---
category: Array
---

# useArrayReduce

Reactive `Array.reduce`.

## Usage

```ts
import { useArrayReduce } from '@vueuse/core';

const sum = useArrayReduce([ref(1), ref(2), ref(3)], (sum, val) => sum + val);
// sum.value: 6
```

### Use with reactive array

```ts
import { useArrayReduce } from '@vueuse/core';

const list = reactive([1, 2]);
const sum = useArrayReduce(list, (sum, val) => sum + val);

list.push(3);
// sum.value: 6
```

### Use with initialValue

```ts
import { useArrayReduce } from '@vueuse/core';

const list = reactive([{ num: 1 }, { num: 2 }]);
const sum = useArrayReduce(list, (sum, val) => sum + val.num, 0);
// sum.value: 3
```

## Type Declarations

```ts
export type UseArrayReducer<PV, CV, R> = (
  previousValue: PV,
  currentValue: CV,
  currentIndex: number,
) => R;
export type UseArrayReduceReturn<T = any> = ComputedRef<T>;
/**
 * Reactive `Array.reduce`
 *
 * @see https://vueuse.org/useArrayReduce
 * @param list - the array was called upon.
 * @param reducer - a "reducer" function.
 *
 * @returns the value that results from running the "reducer" callback function to completion over the entire array.
 *
 * @__NO_SIDE_EFFECTS__
 */
export declare function useArrayReduce<T>(
  list: MaybeRefOrGetter<MaybeRefOrGetter<T>[]>,
  reducer: UseArrayReducer<T, T, T>,
): UseArrayReduceReturn<T>;
/**
 * Reactive `Array.reduce`
 *
 * @see https://vueuse.org/useArrayReduce
 * @param list - the array was called upon.
 * @param reducer - a "reducer" function.
 * @param initialValue - a value to be initialized the first time when the callback is called.
 *
 * @returns the value that results from running the "reducer" callback function to completion over the entire array.
 *
 * @__NO_SIDE_EFFECTS__
 */
export declare function useArrayReduce<T, U>(
  list: MaybeRefOrGetter<MaybeRefOrGetter<T>[]>,
  reducer: UseArrayReducer<U, T, U>,
  initialValue: MaybeRefOrGetter<U>,
): UseArrayReduceReturn<U>;
```
