JSFiddle - React, Tailwind, and code Playground

JavaScript

urlBuilder = (function () {
  'use strict';
  function urlBuilder () {}
  urlBuilder.prototype.urlBase = "http://my.default.domain/";
  urlBuilder.prototype.build = function(relUrl) {
    return this.urlBase + relUrl;
  };
  return urlBuilder;
})();
var builder = new urlBuilder();
builder.urlBase = "http://stackoverflow.com";
console.log(builder.build('/questions')); // prints "http://stackoverflow.com/questions"