### Nth element of 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 nth = (arr, n=0) => (n>0? arr.slice(n,n+1) : arr.slice(n))[0];
// nth(['a','b','c'],1) -> 'b'
// nth(['a','b','b']-2) -> 'a'
```