document.getElementById('loginForm').addEventListener('submit', async function(e) { 
    e.preventDefault(); 
    const username = document.getElementById('username').value.trim(); 
    const password = document.getElementById('password').value.trim(); 
    
    if (!username || !password) { 
        alert('請輸入帳號與密碼'); 
        return; 
    } 
    
    try { 
        // 確保路徑與後端 app.post('/api/login') 一致
        const response = await fetch('/api/login', { 
            method: 'POST', 
            headers: { 'Content-Type': 'application/json' }, 
            body: JSON.stringify({ username, password }) 
        }); 
        
        const data = await response.json(); 
        
        if (data.success) { 
            localStorage.setItem('isLoggedIn', 'true'); 
            localStorage.setItem('username', data.user.username);
            // 登入成功跳轉至後台頁面
            window.location.href = '/admin'; 
        } else { 
            alert(data.error || '登入失敗，請檢查帳號密碼'); 
        } 
    } catch (error) { 
        alert('無法連線至伺服器，請確認 Node.js 程式是否已啟動'); 
        console.error('Error:', error); 
    } 
});