简易计算器

// 使用 ES6 类和模块化
class Calculator {
    constructor() {
        this.display = document.getElementById('display');
        this.currentValue = '0';
        this.previousValue = '';
        this.operation = null;
        this.shouldResetScreen = false;
        this.initializeEventListeners();
    }

    updateDisplay() {
        this.display.value = this.currentValue;
    }

    appendNumber(number) {
        if (this.currentValue.replace('.', '').length >= 12) return;
        if (this.currentValue === '0' || this.shouldResetScreen) {
            this.currentValue = number;
            this.shouldResetScreen = false;
        } else {
            this.currentValue += number;
        }
        this.updateDisplay();
    }

    appendOperator(operator) {
        if (this.operation !== null) this.calculate();
        this.previousValue = this.currentValue;
        this.operation = operator;
        this.shouldResetScreen = true;
    }

    calculate() {
        if (this.operation === null || this.shouldResetScreen) return;
        const prev = parseFloat(this.previousValue);
        const current = parseFloat(this.currentValue);

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

        const result = this.performCalculation(prev, current);
        this.currentValue = result.toString();
        this.operation = null;
        this.previousValue = '';
        this.shouldResetScreen = true;
        this.updateDisplay();
    }

    performCalculation(prev, current) {
        switch (this.operation) {
            case '+': return prev + current;
            case '-': return prev - current;
            case '×': return prev * current;
            case '÷': return prev / current;
            default: return current;
        }
    }
}