# Vector angle

JavaScript, Math · Jan 7, 2021

Calculates the angle (theta) between two vectors.

- Use
`Array.prototype.reduce()`

,`Math.pow()`

and`Math.sqrt()`

to calculate the magnitude of each vector and the scalar product of the two vectors. - Use
`Math.acos()`

to calculate the arccosine and get the theta value.

```
const vectorAngle = (x, y) => {
let mX = Math.sqrt(x.reduce((acc, n) => acc + Math.pow(n, 2), 0));
let mY = Math.sqrt(y.reduce((acc, n) => acc + Math.pow(n, 2), 0));
return Math.acos(x.reduce((acc, n, i) => acc + n * y[i], 0) / (mX * mY));
};
```

`vectorAngle([3, 4], [4, 3]); // 0.283794109208328`