// Creates the Calculator Object
function Calculator() {
    this.number1 = 0;
    this.number2 = 0;
    this.op = 'add';
    this.add = function() { return this.number1 + this.number2; }
    this.minus = function() { return this.number1 - this.number2; }
    this.multiply = function() { return this.number1 * this.number2; }
    this.divide = function() { return this.number1 / this.number2; }
    this.Calculate = function getResult() {
        if (this.op === 'add') return this.add();
        if (this.op === "mult") return this.multiply();
        if (this.op === "minus") return this.minus();
        if (this.op === "div") return this.divide()
    }
}

// Create Event Listener for button
document.getElementById('calculate').addEventListener('click', getResult, false);

// Instantiate Calculator
let calculator = new Calculator();

// Validates input and sets disabled input box to result
function getResult() {
    // handler function for the calcButton
    if (document.getElementById("num1").value === "") {
        // show error or make a page element show the error
        alert("Enter some values")
        return;
    }
    // Give object variables values.
    calculator.number1 = parseFloat(document.getElementById("num1").value);
    calculator.number2 = parseFloat(document.getElementById("num2").value);
    calculator.op = document.getElementById("operator").value;
    // This is pretty cool, + typecasts to Number, I multiply by 100, then divide by 100,
    // while avoiding rounding errors!
    document.getElementById('result').value = +(Math.round(calculator.Calculate() + "e+2") + "e-2");
}