Nodejs Utililty Methods String Empty Check

String.prototype.isNullOrEmpty = function() {
  return (!this || 0 === this.length || /^\s*$/.test(this));  
};

String.prototype.isNullOrEmpty = function(){
    return !(this && this.length > 0);
};

String.prototype.isNullOrEmpty = function () {
  return this === null || this.length === 0;
};

function isNullOrEmptyString(obj) {
  if (isNullOrUnderdefined(obj))
    return false;
  if (isStringType(obj)) {
    return obj.length == 0;
  return false;

String.prototype.isNullOrWhitespace = function () {
  return this === null || this.replace(/\s/g, '').length === 0;
};

String.isNullOrWhitespace = function( input ) {
  return !input || !input.trim();
};

String.prototype.isEmpty = function() {
  return this == '';
};

String.prototype.isEmpty = function() {
    return (this.length === 0 || !this.trim());
};

"use strict";
String.prototype.isEmpty = function() {
    return (this.length === 0 || !this.trim());
};

String.prototype.isEmpty = function() {
  return this.length === 0 || !this.trim();
};