This function will automatically insert commas after the thousands place of any number. Returns a string. Useful for calculations that appear in copy. Call 'commaify(some_dynamic_integer);'

commaify.js

function commaify (num) {
  var num_string, 
    i,
    len,
    threes = [],
    remainders;

  num_string = num.toString();
  len = num_string.length;
  remainders = len % 3;

    
  if (remainders != 0) {
    threes.push(num_string.substr(0, remainders));
  }

  for (i = remainders; i < len; i += 3) {
    threes.push(num_string.substr(i, 3));
  }

  return threes.join();
}