Nodejs Utililty Methods Number Format Pad

Number.prototype.zeroPad = function (len) {
  var s = String(this);
  var c = '0';
  len = len || 2;
  while (s.length < len) {
    s = c + s;
  return s;
};
...

Number.prototype.zeropad = function(n) {
   var str = "" + this;
   var len = n - str.length;
   var pad = "";
   while (len-- > 0) {
      pad += "0";
   return pad + str;
};
...

Number.prototype.zf = function(len){
    if(isNaN(len)) len = 2;
    return (this + '').pad(len, '0');
};

Number.prototype.zfill = function(length) { 
    var str = this.toString();
    if (str.length < length) {
        for(var i = 0; i < length - str.length; i++) str = '0' + str
    return str;
};

Number.prototype.zfill = function (n) {
    var str = String(this);
    while (str.length < n) {
        str = "0" + str;
    return str;
};