# Max array value based on function

JavaScript, Math, Array · Oct 21, 2020

Returns the maximum value of an array, after mapping each element to a value using the provided function.

- Use
`Array.prototype.map()`

to map each element to the value returned by`fn`

. - Use
`Math.max()`

to get the maximum value.

```
const maxBy = (arr, fn) =>
Math.max(...arr.map(typeof fn === 'function' ? fn : val => val[fn]));
```

```
maxBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], x => x.n); // 8
maxBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'); // 8
```