Format numbers as comma-delimited strings

number_with_delimiter.js

//= require <prototype>
// (2001000).withDelimiters();      // "2,001,000"
// (9821).withDelimiters("_");      // "9_821"
// (1221).withDelimiters(",", 100); // "12,21"

Number.prototype.withDelimiters = function(s, k) {
  if (!s) s = ",";
  if (!k) k = 1000;
  var o = [],
      i = Math.floor(this);
  while(i) {
    o.unshift(i % k);
    i = Math.floor(i / k);
  }
  return [ o.shift() ].concat(o.map(function(t) {
    return t.toPaddedString(((k - 1) + '').length);
  })).join(s);
};

value.toFixed(0).replace(/(\d)(?=(\d\d\d)+(?!\d))/g, "$1,")