function Calc(){

  var res = 0;

  var called = '';

​

  function method(val) {

    return method[called](val);

  }

​

  method.add = function add(x) {

    if (!isNaN(x)) res += x;

    called = 'add';

    return this;

  };

  method.subtract = function(x) {

    if (!isNaN(x)) res -= x;

    called = 'subtract';

    return this;

  };

​

  method.divide = function(x) {

    if ((!isNaN(x)) && (x !== 0)) res /= x;

    called = 'divide';

    return this;

  };

  method.multiply = function(x) {

    if (!isNaN(x)) res *= x;

    called = 'multiply';

    return this;

  };

​

  method.reset = function() {

    res = 0;

    called = 'reset';

    return this;

  };

​

  method.getResult = function() {

    return res;

  };

​

  return method;

}

var Calculator = Calc();

​

const result = Calculator.add(100)(10)

    .multiply(2)(2)

    .divide(20)(2)

    .reset()

    .add(8)(4)(42)

    .subtract(1)(1)(10)

    .getResult();

​

console.log(result); // 42