calculator/script.js at main · Rowdy-Rooster/calculator · GitHub

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let display = document.getElementById('display');
let currentInput = '';
let previousInput = '';
let operation = null;
let shouldResetDisplay = false;

function appendNumber(num) {
    if (shouldResetDisplay) {
        currentInput = num;
        shouldResetDisplay = false;
    } else {
        currentInput += num;
    }
    updateDisplay();
}

function appendOperator(op) {
    if (currentInput === '') return;

    if (operation !== null && !shouldResetDisplay) {
        calculate();
    }

    previousInput = currentInput;
    operation = op;
    shouldResetDisplay = true;
    updateDisplay();
}

function calculate() {
    if (operation === null || currentInput === '' || previousInput === '') return;

    let result;
    const prev = parseFloat(previousInput);
    const current = parseFloat(currentInput);

    switch (operation) {
        case '+':
            result = prev + current;
            break;
        case '-':
            result = prev - current;
            break;
        case '*':
            result = prev * current;
            break;
        case '/':
            result = current !== 0 ? prev / current : 0;
            break;
        case '.':
            return;
        default:
            return;
    }

    currentInput = result.toString();
    operation = null;
    previousInput = '';
    shouldResetDisplay = true;
    updateDisplay();
}

function clearDisplay() {
    currentInput = '';
    previousInput = '';
    operation = null;
    shouldResetDisplay = false;
    updateDisplay();
}

function deleteLast() {
    currentInput = currentInput.slice(0, -1);
    updateDisplay();
}

function updateDisplay() {
    if (operation !== null) {
        display.value = previousInput + ' ' + operation + ' ' + currentInput;
    } else {
        display.value = currentInput || '0';
    }
}

// Keyboard support
document.addEventListener('keydown', (e) => {
    if (e.key >= '0' && e.key <= '9') appendNumber(e.key);
    if (e.key === '.') appendOperator('.');
    if (e.key === '+') appendOperator('+');
    if (e.key === '-') appendOperator('-');
    if (e.key === '*') appendOperator('*');
    if (e.key === '/') {
        e.preventDefault();
        appendOperator('/');
    }
    if (e.key === 'Enter' || e.key === '=') {
        e.preventDefault();
        calculate();
    }
    if (e.key === 'Backspace') deleteLast();
    if (e.key === 'Escape') clearDisplay();
});