chaining-design-pattern.js

// Code goes here

var Calc = function (start) {
  var that = this;
  this.add = function(x) {
    start = start + x;
    return that;
  };
  
  this.multiply = function (x) {
    start = start * x;
    return that;
  };
  
  this.equals = function(callback) {
    callback(start);
    return that;
  };
}

new Calc(0)
  .add(1)
  .add(2)
  .multiply(3)
  .multiply(2)
  .equals(function (result) {
    console.log(result);
  });