---
title: copySign
tags: math,beginner
---

Returns the absolute value of the first number, but the sign of the second.

- Use `Math.sign()` to check if the two numbers have the same sign.
- Return `x` if they do, `-x` otherwise.

```js
const copySign = (x, y) => Math.sign(x) === Math.sign(y) ? x : -x;
```

```js
copySign(2, 3); // 2
copySign(2, -3); // -2
copySign(-2, 3); // 2
copySign(-2, -3); // -2
```