funny... built a solution that improves on this solution, then I read thesse comments lol... Solution below.

/*

• DISCLAIMER: This solution is an improvement upon @mdumic 's

• (Current leading solution in the "Best-Practices" category).

• This solution utilizes ES6's Template Literal & does not mutate the input Array.
  */

function createPhoneNumber(numbers){
let newNums = numbers.join('');
return (${newNums.substring(0, 3)})
+ ' ' + newNums.substring(3, 6)
+ '-' + newNums.substring(6);
};

funny... built a solution that improves on this solution, then I read thesse comments lol... Solution below.

/*

• DISCLAIMER: This solution is an improvement upon @mdumic 's

• (Current leading solution in the "Best-Practices" category).

• This solution utilizes ES6's Template Literal & does not mutate the input Array.
  */

function createPhoneNumber(numbers){
let newNums = numbers.join('');
return (${newNums.substring(0, 3)})
+ ' ' + newNums.substring(3, 6)
+ '-' + newNums.substring(6);
};

funny... built a solution that improves on this solution, then I read thesse comments lol... Solution below.