phonenumbers

/*
another simple one.  can't wait to see the other submissions to see how even simpler it could have been.
I really liked this solution.  it created a format and then filled in the x's with the numbers from the array.  I wonder how it does for speed?
function createPhoneNumber(numbers){
  var format = "(xxx) xxx-xxxx";
  
  for(var i = 0; i < numbers.length; i++)
  {
    format = format.replace('x', numbers[i]);
  }
  
  return format;
}

I like this one as well.  It used substring feature of the arrays to create it.

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

of course there were capture group examples as well using regex.  that may be the most elegant.  I'll have to compare to see which one is speediest.
*/

function createPhoneNumber(numbers){
  //add first parenthesis
  numbers.splice(0,0,'(');
  //add second parenthesis and space
  numbers.splice(4,0,') ');
  //add dash
  numbers.splice(8,0,'-');
  //return joined together.
  return numbers.join('');
}