---
category: '@Math'
related: createGenericProjection
---

# useProjection

Reactive numeric projection from one domain to another.

## Usage

```ts
import { useProjection } from '@vueuse/math';

const input = ref(0);
const projected = useProjection(input, [0, 10], [0, 100]);

input.value = 5; // projected.value === 50
input.value = 10; // projected.value === 100
```

## Type Declarations

```ts
/**
 * Reactive numeric projection from one domain to another.
 *
 * @see https://vueuse.org/useProjection
 *
 * @__NO_SIDE_EFFECTS__
 */
export declare function useProjection(
  input: MaybeRefOrGetter<number>,
  fromDomain: MaybeRefOrGetter<readonly [number, number]>,
  toDomain: MaybeRefOrGetter<readonly [number, number]>,
  projector?: ProjectorFunction<number, number>,
): ComputedRef<number>;
```
