do the maths

calculate.js

(function() {

  "use strict";

  var calculatorPrototype = {

      total: 0,

      add: function add(number) {

        this.total += number;

        return this;

      },
      subtract: function subtract(number) {

        this.total -= number;
        return this;

      },
      multiply: function multiply(number) {

        this.total = this.total * number;
        return this;

      },
      pow: function pow(number) {

        this.total = Math.pow(this.total, number);
        return this;

      },
      square: function square() {

        this.total = this.total * this.total;
        return this;

      },
      divide: function divide(number) {

        this.total = this.total / number;
        return this;

      },
      get: function get() {

        return this.total;

      }

  };

  function calculator(base, proto) {

    var baseNumber = base || 0;
    var calcProto = Object.create(proto);

    calcProto.total = baseNumber;

    return calcProto;

  }

  var calculate = calculator(10, calculatorPrototype);

  calculate.add(5).add(5).divide(2).pow(2).square();

  console.log(calculate.get());

})();