### nthElement

Returns the nth element of an array.

Use `Array.slice()` to get an array containing the nth element at the first place.
If the index is out of bounds, return `[]`.
Omit the second argument, `n`, to get the first element of the array.

```js
const nthElement = (arr, n=0) => (n>0? arr.slice(n,n+1) : arr.slice(n))[0];
```

```js
nthElement(['a','b','c'],1) // 'b'
nthElement(['a','b','b'],-3) // 'a'
```