kalkulator.js

const calculator = {
    displayNumber:'0',
    operator: null,
    firstNumber: null,
    waitingForSecondNumber: false
};

function updateDisplay(){
    document.querySelector('#displayNumber').innerText = calculator.displayNumber;
}

function clearCalculator(){
    calculator.displayNumber = '0';
    calculator.operator = null;
    calculator.firstnumber = null;
    calculator.waitingForSecondNumber=false
}

function inputDigit(digit) {
    if (calculator.displayNumber === '0') {
        calculator.displayNumber = digit;
    } else {
        calculator.displayNumber += digit;
    }
}

function inverseNumber() {
    if (calculator.displayNumber === '0') {
        return;
    }
    calculator.displayNumber = calculator.displayNumber * -1;
}

function handleOperator(operator){
    if(!calculator.waitingForSecondNumber) {
        calculator.operator = operator;
        calculator.waitingForSecondNumber = true;
        calculator.firstNumber = calculator.displayNumber;

        //mengatur ulang nilai display number supaya tombol selanjutnya dimulai dari angka pertama lagi
        calculator.displayNumber = '0';
    } else {
        alert('Operator sudah ditetapkan')
    }
}

function performCalculation() {
    if (calculator.firstNumber == null || calculator.operator == null) {
        alert("Anda belum menetapkan operator");
        return;
    }

    let result = 0;
    if (calculator.operator === "+") {
        result = parseInt(calculator.firstNumber) + parseInt(calculator.displayNumber);
    } else {
        result = parseInt(calculator.firstNumber) - parseInt(calculator.displayNumber)
    }
    calculator.displayNumber = result;
}

const buttons = document.querySelectorAll(".button");
for (let button of buttons) {
    button.addEventListener('click', function(event) {

        //mendapatkan objek elemen yang diklik
        const target = event.target;

        if(target.classList.contains('clear')){
            clearCalculator();
            updateDisplay();
            return;
        }

        if(target.classList.contains('negative')){
            inverseNumber();
            updateDisplay();
            return;
        }

        if(target.classList.contains('equals')){
            performCalculation();
            updateDisplay();
            return;
        }

        if(target.classList.contains('operator')){
            hadleOperator(target.innerText);
            return;
        }

        inputDigit(target.innerText);
        updateDisplay()
    });
}