JS - add Comma to number and remove decimal

Question

numberWithCommas: function(x) {
  return x.toFixed(0).replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}

//e.g .00
return x.toFixed(2) //----> output 10,000.00

//e.g .0
return x.toFixed(1) //----> output 10,000.0