Test completion suggestion for calculator (Challenge 01/03)

[wim-va]

The test as-is didn't cover faulty operator handling, so I came up with

// calculator.test.js
// Division
...
// Error case: Invalid operator
  expect(() => calculator(num1, num2, "//")).toThrow("Invalid operator");

Adding the error throwing handling naturally requires the main file to throw an error in this case. I used the default for that:

function calculator(num1, num2, operator) {
    switch (operator) {
        case "+": return num1 + num2;
        case "-": return num1 - num2;
        case "*": return num1 * num2;
        case "/": return num1 / num2;
        default: throw new Error('Invalid operator');
    }
}

This way, anything other than the operators throws an error. You're welcome to use it, if you choose.