TotalCalculator

// TotalCalculator.js
function TotalCalculator() {
}

TotalCalculator.prototype.calculate = function(quantity, price) {
  var _quantity = parseInt(quantity);
  if (isNaN(_quantity))
    return 'N/A';

  var _price = parseInt(price.replace('$', ''));
  var total = _quantity * _price;
  return '$' + total.toFixed(2);
}

// TotalCalculatorSpec.js
describe("TotalCalculator", function() {
  var totalCalculator;

  beforeEach(function() {
    totalCalculator = new TotalCalculator();
  });

  it('calculates total from integer strings', function() {
    var result = totalCalculator.calculate('2', '$15.00');
    expect(result).toEqual('$30.00');
  });

  it('calculates total from double string', function() {
    var result = totalCalculator.calculate('2.3', '$15.00');
    expect(result).toEqual('$30.00');
  });

  it('handles non-numeric quantity', function() {
    var result = totalCalculator.calculate('He', '$15.00');
    expect(result).toEqual('N/A');
  });
});