phoneNumbers

let arr=[1,2,3,4,5,6,7,8,9]
arr.splice(0,0,'(')
arr.splice(4,0,')')
arr.splice(5,0,' ')
arr.splice(9,0,'-')
console.log(arr.join(''))

// function createPhoneNumber(numbers){
//   var format = "(xxx) xxx-xxxx";
  
//   for(var i = 0; i < numbers.length; i++)
//   {
//     format = format.replace('x', numbers[i]);
//   }
  
//   return format;
// }