Double, isEven, getFileExtension, longestString, arraySum fun functions

SlickPractice.js

'use strict';

function doubleInteger( i ) {
	// i will be an integer. Double it and return it.
	return i * 2;
}

function isNumberEven( i ) {
	// i will be an integer. Return true if it's even, and false if it isn't.
	return ( i % 2 === 0 );
}

function getFileExtension( i ) {
	// i will be a string, but it may not have a file extension.
	// return the file extension (with no period) if it has one, otherwise false
	return ( i.split( '.' ).length > 1 ) ? i.substr( i.lastIndexOf( '.' ) + 1 ) : false;
}

function longestString( i ) {
	// i will be an array.
	// return the longest string in the array
	return i.sort( ( a, b ) => {
	    if( typeof a === 'string' && typeof b === 'string' ) {
		    return a.length - b.length;
	    }
	}).pop();
}

function arraySum( i ) {
	// i will be an array, containing integers, strings and/or arrays like itself.
	// Sum all the integers you find, anywhere in the nest of arrays.
	return i.reduce( ( x, y ) => {
		return ( !!y.length ) ? ( typeof y === 'object' ) ? x + arraySum( y ) : x : ( typeof y === 'number' ) ? x + y : x;
	}, 0 );
}