Calculator/script.js at main · HugosGitStuff/Calculator · GitHub

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let currentOperand = '0';
let previousOperand = '';
let operation = undefined;
let shouldResetDisplay = false;

const currentOperandElement = document.querySelector('.current-operand');
const previousOperandElement = document.querySelector('.previous-operand');

function clearAll() {
    currentOperand = '0';
    previousOperand = '';
    operation = undefined;
    shouldResetDisplay = false;
    updateDisplay();
}

function deleteNumber() {
    if (currentOperand === '0') return;
    if (currentOperand.length === 1) {
        currentOperand = '0';
    } else {
        currentOperand = currentOperand.slice(0, -1);
    }
    updateDisplay();
}

function appendNumber(number) {
    if (shouldResetDisplay) {
        currentOperand = '';
        shouldResetDisplay = false;
    }
    if (number === '.' && currentOperand.includes('.')) return;
    if (currentOperand === '0' && number !== '.') {
        currentOperand = number;
    } else {
        currentOperand += number;
    }
    updateDisplay();
}

function appendOperator(operator) {
    if (currentOperand === '') return;
    if (previousOperand !== '') {
        calculate();
    }
    operation = operator;
    previousOperand = currentOperand;
    currentOperand = '';
    shouldResetDisplay = false;
    updateDisplay();
}

function calculate() {
    let computation;
    const prev = parseFloat(previousOperand);
    const current = parseFloat(currentOperand);

    if (isNaN(prev) || isNaN(current)) return;

    switch (operation) {
        case '+':
            computation = prev + current;
            break;
        case '-':
            computation = prev - current;
            break;
        case '×':
            computation = prev * current;
            break;
        case '÷':
            if (current === 0) {
                alert('Cannot divide by zero!');
                clearAll();
                return;
            }
            computation = prev / current;
            break;
        case '%':
            computation = (prev * current) / 100;
            break;
        default:
            return;
    }

    currentOperand = computation.toString();
    operation = undefined;
    previousOperand = '';
    shouldResetDisplay = true;
    updateDisplay();
}

function updateDisplay() {
    currentOperandElement.textContent = currentOperand;
    if (operation != null) {
        previousOperandElement.textContent = `${previousOperand} ${operation}`;
    } else {
        previousOperandElement.textContent = previousOperand;
    }
}