### isArmstrongNumber

Checks if the given number is an Armstrong number or not.

Convert the given number into an array of digits. Use `Math.pow()` to get the appropriate power for each digit and sum them up. If the sum is equal to the number itself, return `true` otherwise `false`.

```js
const isArmstrongNumber = digits => 
  ( arr => arr.reduce( ( a, d ) => a + Math.pow( parseInt( d ), arr.length ), 0 ) == digits ? true : false )( ( digits+'' ).split( '' ) );
// isArmstrongNumber(1634) -> true
// isArmstrongNumber(371) -> true
// isArmstrongNumber(56) -> false
```