Connection Status

The Connection Status component monitors and reacts to changes in the user's internet connection status. This component provides a simple yet powerful way to adapt your application's behavior when the user's device goes offline or comes back online, ensuring a seamless user experience regardless of network conditions.

This component is particularly useful for:

  • Displaying connection status notifications to users

  • Disabling features that require internet connectivity when offline

  • Queueing actions for later when connection is restored

  • Showing offline-specific UI and content

  • Preventing data loss during connectivity issues

  • Providing feedback about network-dependent operations

  • Implementing offline-first application strategies

  • Enhancing Progressive Web App capabilities

Browser Support

The Connection Status API is based on the navigator.onLine property and online/offline events, which are supported by all modern browsers on desktop and mobile platforms.

Support level: Universal - works on all major browsers including Chrome, Firefox, Safari, Edge, and their mobile counterparts.

The navigator.onLine property only indicates whether the browser has a network connection, not whether internet access is actually available. A device might be connected to a local network but have no internet access.

Usage

Basic Connection Status Display

<div {{ stimulus_controller('@pwa/connection-status', {
    onlineMessage: 'You are online',
    offlineMessage: 'You are offline'
}) }}>
    <div {{ stimulus_target('@pwa/connection-status', 'attribute') }}
         class="connection-banner online:bg-green-100 online:text-green-800 offline:bg-red-100 offline:text-red-800"
         role="alert">
        <strong>Connection status:</strong>
        <span {{ stimulus_target('@pwa/connection-status', 'message') }}>
            Detecting connection...
        </span>
    </div>
</div>

Styled Connection Notification

<div {{ stimulus_controller('@pwa/connection-status', {
    onlineMessage: '✓ Connected to the internet',
    offlineMessage: '⚠ No internet connection'
}) }}>
    <div {{ stimulus_target('@pwa/connection-status', 'attribute') }}
         {{ stimulus_target('@pwa/connection-status', 'message') }}
         class="fixed top-4 right-4 p-4 rounded-lg shadow-lg transition-all duration-300
                online:bg-green-50 online:text-green-900 online:border-green-200
                offline:bg-yellow-50 offline:text-yellow-900 offline:border-yellow-200"
         style="border-width: 2px;">
    </div>
</div>

<style>
    [data-connection-status="ONLINE"] {
        animation: slideIn 0.3s ease-out;
    }

    [data-connection-status="OFFLINE"] {
        animation: slideIn 0.3s ease-out, pulse 2s infinite;
    }

    @keyframes slideIn {
        from {
            transform: translateX(100%);
            opacity: 0;
        }
        to {
            transform: translateX(0);
            opacity: 1;
        }
    }

    @keyframes pulse {
        0%, 100% {
            opacity: 1;
        }
        50% {
            opacity: 0.7;
        }
    }
</style>

Conditional Feature Display

<div {{ stimulus_controller('@pwa/connection-status') }}>
    <!-- Main content area with connection-aware features -->
    <div {{ stimulus_target('@pwa/connection-status', 'attribute') }}>

        <!-- Online-only features -->
        <div class="online:block offline:hidden">
            <h2>Live Features</h2>
            <button class="btn-primary">Sync Now</button>
            <button class="btn-primary">Upload Files</button>
            <button class="btn-primary">Share Content</button>
        </div>

        <!-- Offline message -->
        <div class="online:hidden offline:block">
            <div class="offline-notice">
                <h2>Offline Mode</h2>
                <p>Some features are unavailable while offline.</p>
                <p>Your changes will be saved and synced when you reconnect.</p>
            </div>
        </div>

        <!-- Always available features -->
        <div class="mt-6">
            <h2>Available Offline</h2>
            <button class="btn-secondary">View Saved Content</button>
            <button class="btn-secondary">Edit Drafts</button>
        </div>
    </div>

    <!-- Status indicator -->
    <div class="status-bar" {{ stimulus_target('@pwa/connection-status', 'attribute') }}>
        <span {{ stimulus_target('@pwa/connection-status', 'message') }}></span>
    </div>
</div>

<style>
    .online\:block { display: none; }
    [data-connection-status="ONLINE"] .online\:block { display: block; }

    .online\:hidden { display: block; }
    [data-connection-status="ONLINE"] .online\:hidden { display: none; }

    .offline\:block { display: none; }
    [data-connection-status="OFFLINE"] .offline\:block { display: block; }

    .offline\:hidden { display: block; }
    [data-connection-status="OFFLINE"] .offline\:hidden { display: none; }

    .offline-notice {
        padding: 20px;
        background: #fef3c7;
        border: 2px solid #f59e0b;
        border-radius: 8px;
        text-align: center;
    }

    .status-bar {
        position: fixed;
        bottom: 0;
        left: 0;
        right: 0;
        padding: 10px;
        text-align: center;
        font-weight: 500;
        transition: all 0.3s;
    }

    [data-connection-status="ONLINE"] .status-bar {
        background: #d1fae5;
        color: #065f46;
    }

    [data-connection-status="OFFLINE"] .status-bar {
        background: #fef3c7;
        color: #92400e;
    }
</style>

Form Behavior Based on Connection

<div {{ stimulus_controller('@pwa/connection-status') }}>
    <form id="contact-form" {{ stimulus_target('@pwa/connection-status', 'attribute') }}>
        <h2>Contact Us</h2>

        <div class="form-group">
            <label for="name">Name</label>
            <input type="text" id="name" name="name" required>
        </div>

        <div class="form-group">
            <label for="email">Email</label>
            <input type="email" id="email" name="email" required>
        </div>

        <div class="form-group">
            <label for="message">Message</label>
            <textarea id="message" name="message" required></textarea>
        </div>

        <!-- Online: normal submit button -->
        <button type="submit" class="online:block offline:hidden">
            Send Message
        </button>

        <!-- Offline: save draft button -->
        <button type="button" class="online:hidden offline:block" onclick="saveDraft()">
            Save Draft (Offline)
        </button>

        <!-- Status message -->
        <div class="form-status" {{ stimulus_target('@pwa/connection-status', 'attribute') }}>
            <span class="online:inline offline:hidden">
                ✓ Ready to send
            </span>
            <span class="online:hidden offline:inline">
                ⚠ Offline - your message will be saved as draft
            </span>
        </div>
    </form>
</div>

<script>
    function saveDraft() {
        const formData = {
            name: document.getElementById('name').value,
            email: document.getElementById('email').value,
            message: document.getElementById('message').value,
            savedAt: new Date().toISOString()
        };

        localStorage.setItem('contactFormDraft', JSON.stringify(formData));
        alert('Draft saved! It will be sent when you\'re back online.');
    }

    // Auto-submit drafts when connection is restored
    document.addEventListener('pwa--connection-status:status-changed', (event) => {
        if (event.detail.status === 'ONLINE') {
            const draft = localStorage.getItem('contactFormDraft');
            if (draft) {
                if (confirm('You have a saved draft. Would you like to send it now?')) {
                    const data = JSON.parse(draft);
                    // Submit the form
                    // ... your submit logic here
                    localStorage.removeItem('contactFormDraft');
                }
            }
        }
    });
</script>

Action Queue for Offline Operations

<div {{ stimulus_controller('@pwa/connection-status') }}>
    <div class="task-manager">
        <h2>Task Manager</h2>

        <div class="connection-status" {{ stimulus_target('@pwa/connection-status', 'attribute') }}>
            <span {{ stimulus_target('@pwa/connection-status', 'message') }}></span>
        </div>

        <div id="pending-queue" class="online:hidden offline:block">
            <p>Pending actions: <span id="queue-count">0</span></p>
        </div>

        <button onclick="performAction('Task completed')">Complete Task</button>
        <button onclick="performAction('New item added')">Add Item</button>
        <button onclick="performAction('Settings updated')">Update Settings</button>

        <div id="action-log"></div>
    </div>
</div>

<script>
    const actionQueue = [];
    let isOnline = navigator.onLine;

    document.addEventListener('pwa--connection-status:status-changed', (event) => {
        isOnline = event.detail.status === 'ONLINE';

        if (isOnline && actionQueue.length > 0) {
            processQueue();
        }

        updateQueueDisplay();
    });

    function performAction(action) {
        const actionItem = {
            action: action,
            timestamp: new Date().toISOString(),
            id: Date.now()
        };

        if (isOnline) {
            // Process immediately
            sendToServer(actionItem);
        } else {
            // Queue for later
            actionQueue.push(actionItem);
            updateQueueDisplay();
            logAction(`⏳ Queued: ${action}`, 'warning');
        }
    }

    function sendToServer(actionItem) {
        // Simulate server request
        console.log('Sending to server:', actionItem);
        logAction(`✓ Sent: ${actionItem.action}`, 'success');

        // In a real app, you would do:
        // fetch('/api/actions', {
        //     method: 'POST',
        //     body: JSON.stringify(actionItem)
        // });
    }

    function processQueue() {
        const count = actionQueue.length;
        logAction(`🔄 Processing ${count} queued action(s)...`, 'info');

        while (actionQueue.length > 0) {
            const action = actionQueue.shift();
            sendToServer(action);
        }

        updateQueueDisplay();
    }

    function updateQueueDisplay() {
        document.getElementById('queue-count').textContent = actionQueue.length;
    }

    function logAction(message, type) {
        const log = document.getElementById('action-log');
        const entry = document.createElement('div');
        entry.className = `log-entry log-${type}`;
        entry.textContent = `${new Date().toLocaleTimeString()}: ${message}`;
        log.insertBefore(entry, log.firstChild);

        // Keep only last 10 entries
        while (log.children.length > 10) {
            log.removeChild(log.lastChild);
        }
    }
</script>

<style>
    .connection-status {
        padding: 10px;
        margin-bottom: 15px;
        border-radius: 6px;
        font-weight: 500;
    }

    [data-connection-status="ONLINE"] .connection-status {
        background: #d1fae5;
        color: #065f46;
    }

    [data-connection-status="OFFLINE"] .connection-status {
        background: #fef3c7;
        color: #92400e;
    }

    #pending-queue {
        padding: 10px;
        background: #fef3c7;
        border-radius: 6px;
        margin-bottom: 15px;
    }

    .log-entry {
        padding: 8px;
        margin: 5px 0;
        border-radius: 4px;
        font-size: 14px;
    }

    .log-success {
        background: #d1fae5;
        color: #065f46;
    }

    .log-warning {
        background: #fef3c7;
        color: #92400e;
    }

    .log-info {
        background: #dbeafe;
        color: #1e40af;
    }
</style>

Real-Time Sync Indicator

<div {{ stimulus_controller('@pwa/connection-status') }}>
    <div class="editor-container">
        <div class="editor-header" {{ stimulus_target('@pwa/connection-status', 'attribute') }}>
            <h2>Document Editor</h2>

            <div class="sync-status">
                <span class="online:inline offline:hidden">
                    <svg class="icon" viewBox="0 0 20 20" fill="currentColor">
                        <path d="M10 18a8 8 0 100-16 8 8 0 000 16zm3.707-9.293a1 1 0 00-1.414-1.414L9 10.586 7.707 9.293a1 1 0 00-1.414 1.414l2 2a1 1 0 001.414 0l4-4z"/>
                    </svg>
                    Synced
                </span>

                <span class="online:hidden offline:inline">
                    <svg class="icon" viewBox="0 0 20 20" fill="currentColor">
                        <path fill-rule="evenodd" d="M18 10a8 8 0 11-16 0 8 8 0 0116 0zm-7 4a1 1 0 11-2 0 1 1 0 012 0zm-1-9a1 1 0 00-1 1v4a1 1 0 102 0V6a1 1 0 00-1-1z"/>
                    </svg>
                    Not synced (offline)
                </span>
            </div>
        </div>

        <textarea id="editor" placeholder="Start typing..."></textarea>

        <div class="editor-footer">
            <span id="last-saved">Never saved</span>
            <span {{ stimulus_target('@pwa/connection-status', 'message') }}></span>
        </div>
    </div>
</div>

<script>
    const editor = document.getElementById('editor');
    const lastSavedEl = document.getElementById('last-saved');
    let saveTimeout;
    let isOnline = navigator.onLine;

    // Auto-save on typing
    editor.addEventListener('input', () => {
        clearTimeout(saveTimeout);
        saveTimeout = setTimeout(() => {
            saveContent();
        }, 1000);
    });

    // Listen to connection changes
    document.addEventListener('pwa--connection-status:status-changed', (event) => {
        isOnline = event.detail.status === 'ONLINE';

        if (isOnline) {
            syncToServer();
        }
    });

    function saveContent() {
        const content = editor.value;

        if (isOnline) {
            // Save to server
            saveToServer(content);
        } else {
            // Save locally
            localStorage.setItem('editorContent', content);
            lastSavedEl.textContent = `Saved locally at ${new Date().toLocaleTimeString()}`;
        }
    }

    function saveToServer(content) {
        // Simulate server save
        console.log('Saving to server:', content);
        lastSavedEl.textContent = `Synced at ${new Date().toLocaleTimeString()}`;

        // In real app:
        // fetch('/api/save', {
        //     method: 'POST',
        //     body: JSON.stringify({ content })
        // });
    }

    function syncToServer() {
        const localContent = localStorage.getItem('editorContent');
        if (localContent) {
            saveToServer(localContent);
            localStorage.removeItem('editorContent');
        }
    }

    // Load saved content on page load
    window.addEventListener('load', () => {
        const saved = localStorage.getItem('editorContent');
        if (saved) {
            editor.value = saved;
        }
    });
</script>

<style>
    .editor-container {
        max-width: 800px;
        margin: 0 auto;
        border: 1px solid #e5e7eb;
        border-radius: 8px;
        overflow: hidden;
    }

    .editor-header {
        display: flex;
        justify-content: space-between;
        align-items: center;
        padding: 15px 20px;
        border-bottom: 1px solid #e5e7eb;
    }

    [data-connection-status="ONLINE"] .editor-header {
        background: #f0fdf4;
    }

    [data-connection-status="OFFLINE"] .editor-header {
        background: #fef3c7;
    }

    .sync-status {
        display: flex;
        align-items: center;
        gap: 8px;
        font-weight: 500;
    }

    [data-connection-status="ONLINE"] .sync-status {
        color: #16a34a;
    }

    [data-connection-status="OFFLINE"] .sync-status {
        color: #ca8a04;
    }

    .icon {
        width: 20px;
        height: 20px;
    }

    #editor {
        width: 100%;
        min-height: 300px;
        padding: 20px;
        border: none;
        resize: vertical;
        font-family: monospace;
    }

    .editor-footer {
        display: flex;
        justify-content: space-between;
        padding: 10px 20px;
        background: #f9fafb;
        border-top: 1px solid #e5e7eb;
        font-size: 14px;
        color: #6b7280;
    }
</style>

Multiple Status Indicators

<div {{ stimulus_controller('@pwa/connection-status', {
    onlineMessage: 'Online',
    offlineMessage: 'Offline'
}) }}>
    <nav {{ stimulus_target('@pwa/connection-status', 'attribute') }}
         class="navbar online:bg-white offline:bg-gray-100">
        <div class="navbar-brand">My App</div>

        <!-- Multiple message targets -->
        <div class="status-indicator">
            <span class="status-dot online:bg-green-500 offline:bg-red-500"></span>
            <span {{ stimulus_target('@pwa/connection-status', 'message') }}></span>
        </div>
    </nav>

    <main {{ stimulus_target('@pwa/connection-status', 'attribute') }}>
        <aside class="sidebar">
            <div class="sidebar-status">
                Connection: <strong {{ stimulus_target('@pwa/connection-status', 'message') }}></strong>
            </div>
        </aside>

        <div class="content">
            <h1>Dashboard</h1>
            <!-- Your content here -->
        </div>
    </main>

    <footer {{ stimulus_target('@pwa/connection-status', 'attribute') }}
            class="footer online:bg-green-50 offline:bg-red-50">
        <p>Status: <span {{ stimulus_target('@pwa/connection-status', 'message') }}></span></p>
    </footer>
</div>

<style>
    .status-dot {
        display: inline-block;
        width: 10px;
        height: 10px;
        border-radius: 50%;
        margin-right: 8px;
    }

    .sidebar-status {
        padding: 10px;
        background: #f3f4f6;
        border-radius: 6px;
        margin-bottom: 20px;
    }

    [data-connection-status="ONLINE"] .sidebar-status {
        border-left: 4px solid #10b981;
    }

    [data-connection-status="OFFLINE"] .sidebar-status {
        border-left: 4px solid #ef4444;
    }
</style>

Parameters

onlineMessage

Type: string Default: "You are online"

The message displayed when the user is online. This message is injected into all elements marked with the message target.

{{ stimulus_controller('@pwa/connection-status', {
    onlineMessage: 'Connected to the internet ✓'
}) }}

offlineMessage

Type: string Default: "You are offline"

The message displayed when the user is offline. This message is injected into all elements marked with the message target.

{{ stimulus_controller('@pwa/connection-status', {
    offlineMessage: 'No internet connection ⚠'
}) }}

Actions

None - This component automatically monitors connection status without requiring explicit actions.

Targets

message

HTML elements that will display the connection status message. The content of these elements will be replaced with either onlineMessage or offlineMessage depending on the current connection status.

Multiple targets allowed: Yes - you can have multiple message targets throughout your application.

<span {{ stimulus_target('@pwa/connection-status', 'message') }}></span>

attribute

HTML elements that will receive a data-connection-status attribute set to either "ONLINE" or "OFFLINE". This is particularly useful for conditional styling with CSS.

Multiple targets allowed: Yes - you can mark multiple elements with this target.

<div {{ stimulus_target('@pwa/connection-status', 'attribute') }}
     class="online:bg-green-100 offline:bg-red-100">
    <!-- Content -->
</div>

The data-connection-status attribute can be used with CSS attribute selectors:

[data-connection-status="ONLINE"] {
    background-color: #d1fae5;
}

[data-connection-status="OFFLINE"] {
    background-color: #fee2e2;
}

Or with Tailwind CSS variants:

<div class="online:bg-green-100 offline:bg-red-100">

Events

pwa--connection-status:status-changed

Dispatched whenever the connection status changes (online ↔ offline).

Payload:

  • status (string): Either "ONLINE" or "OFFLINE"

  • message (string): The current message (either onlineMessage or offlineMessage)

Example:

document.addEventListener('pwa--connection-status:status-changed', (event) => {
    const { status, message } = event.detail;

    console.log('Connection status:', status);
    console.log('Status message:', message);

    if (status === 'ONLINE') {
        // Connection restored - sync data
        syncPendingChanges();
    } else {
        // Connection lost - enable offline mode
        enableOfflineMode();
    }
});

Best Practices

  1. Provide clear feedback: Always inform users about their connection status

  2. Graceful degradation: Disable online-only features when offline

  3. Queue operations: Store user actions locally and sync when connection is restored

  4. Save drafts: Auto-save content locally to prevent data loss

  5. Visual indicators: Use clear, consistent visual cues for connection status

  6. Don't block: Allow users to continue working offline when possible

  7. Optimize for mobile: Connection status is particularly important on mobile devices

  8. Test thoroughly: Test your application's behavior in various connectivity scenarios

  9. Handle edge cases: Consider slow connections, intermittent connectivity

  10. Inform, don't alarm: Frame offline messages positively when possible

Connection-Aware CSS Patterns

Using Tailwind CSS

If you're using Tailwind CSS, you can create custom variants for connection status:

// tailwind.config.js
module.exports = {
    theme: {
        extend: {}
    },
    plugins: [
        function({ addVariant }) {
            addVariant('online', '[data-connection-status="ONLINE"] &');
            addVariant('offline', '[data-connection-status="OFFLINE"] &');
        }
    ]
}

Then use these variants in your HTML:

<div class="online:bg-green-100 online:text-green-800
            offline:bg-red-100 offline:text-red-800">
    Connection status indicator
</div>

Using Standard CSS

/* Base styles */
.connection-indicator {
    padding: 10px;
    border-radius: 6px;
    font-weight: 500;
    transition: all 0.3s;
}

/* Online state */
[data-connection-status="ONLINE"] .connection-indicator {
    background-color: #d1fae5;
    color: #065f46;
    border-left: 4px solid #10b981;
}

/* Offline state */
[data-connection-status="OFFLINE"] .connection-indicator {
    background-color: #fee2e2;
    color: #991b1b;
    border-left: 4px solid #ef4444;
}

/* Show/hide based on status */
[data-connection-status="ONLINE"] .online-only {
    display: block;
}

[data-connection-status="OFFLINE"] .online-only {
    display: none;
}

[data-connection-status="ONLINE"] .offline-only {
    display: none;
}

[data-connection-status="OFFLINE"] .offline-only {
    display: block;
}

Complete Example: Offline-First Todo App

<div {{ stimulus_controller('@pwa/connection-status', {
    onlineMessage: 'Synced',
    offlineMessage: 'Working offline'
}) }}>
    <div class="todo-app">
        <!-- Header with sync status -->
        <header {{ stimulus_target('@pwa/connection-status', 'attribute') }}
                class="app-header online:bg-green-50 offline:bg-amber-50">
            <h1>Todo App</h1>
            <div class="sync-status">
                <span class="status-icon online:text-green-600 offline:text-amber-600">●</span>
                <span {{ stimulus_target('@pwa/connection-status', 'message') }}></span>
            </div>
        </header>

        <!-- Offline notice -->
        <div {{ stimulus_target('@pwa/connection-status', 'attribute') }}
             class="online:hidden offline:block offline-notice">
            <p>📱 You're working offline. Your changes will sync when you're back online.</p>
        </div>

        <!-- Todo form -->
        <form id="todo-form" onsubmit="addTodo(event)">
            <input type="text" id="todo-input" placeholder="Add a new todo..." required>
            <button type="submit">Add</button>
        </form>

        <!-- Pending sync indicator -->
        <div id="pending-sync" class="online:hidden offline:block pending-sync" style="display: none;">
            <p>⏳ <span id="pending-count">0</span> item(s) waiting to sync</p>
        </div>

        <!-- Todo list -->
        <ul id="todo-list"></ul>
    </div>
</div>

<script>
    let todos = JSON.parse(localStorage.getItem('todos') || '[]');
    let pendingSync = JSON.parse(localStorage.getItem('pendingSync') || '[]');
    let isOnline = navigator.onLine;

    // Listen to connection changes
    document.addEventListener('pwa--connection-status:status-changed', (event) => {
        isOnline = event.detail.status === 'ONLINE';

        if (isOnline && pendingSync.length > 0) {
            syncPendingTodos();
        }

        updatePendingCount();
    });

    function addTodo(event) {
        event.preventDefault();

        const input = document.getElementById('todo-input');
        const todo = {
            id: Date.now(),
            text: input.value,
            completed: false,
            createdAt: new Date().toISOString(),
            synced: isOnline
        };

        todos.push(todo);
        saveTodos();

        if (!isOnline) {
            pendingSync.push({ action: 'create', todo });
            savePendingSync();
        } else {
            syncToServer({ action: 'create', todo });
        }

        input.value = '';
        renderTodos();
    }

    function toggleTodo(id) {
        const todo = todos.find(t => t.id === id);
        if (todo) {
            todo.completed = !todo.completed;
            saveTodos();

            if (!isOnline) {
                pendingSync.push({ action: 'update', todo });
                savePendingSync();
            } else {
                syncToServer({ action: 'update', todo });
            }

            renderTodos();
        }
    }

    function deleteTodo(id) {
        const todo = todos.find(t => t.id === id);
        todos = todos.filter(t => t.id !== id);
        saveTodos();

        if (!isOnline) {
            pendingSync.push({ action: 'delete', todo });
            savePendingSync();
        } else {
            syncToServer({ action: 'delete', todo });
        }

        renderTodos();
    }

    function saveTodos() {
        localStorage.setItem('todos', JSON.stringify(todos));
    }

    function savePendingSync() {
        localStorage.setItem('pendingSync', JSON.stringify(pendingSync));
        updatePendingCount();
    }

    function updatePendingCount() {
        const count = pendingSync.length;
        document.getElementById('pending-count').textContent = count;
        document.getElementById('pending-sync').style.display = count > 0 ? 'block' : 'none';
    }

    function syncToServer(change) {
        // Simulate server sync
        console.log('Syncing to server:', change);

        // In a real app:
        // fetch('/api/todos', {
        //     method: 'POST',
        //     headers: { 'Content-Type': 'application/json' },
        //     body: JSON.stringify(change)
        // });
    }

    function syncPendingTodos() {
        console.log(`Syncing ${pendingSync.length} pending changes...`);

        pendingSync.forEach(change => {
            syncToServer(change);
        });

        pendingSync = [];
        savePendingSync();

        // Mark all todos as synced
        todos.forEach(todo => todo.synced = true);
        saveTodos();
        renderTodos();
    }

    function renderTodos() {
        const list = document.getElementById('todo-list');
        list.innerHTML = todos.map(todo => `
            <li class="todo-item ${todo.completed ? 'completed' : ''}">
                <input type="checkbox"
                       ${todo.completed ? 'checked' : ''}
                       onchange="toggleTodo(${todo.id})">
                <span class="todo-text">${todo.text}</span>
                ${!todo.synced ? '<span class="sync-badge">Not synced</span>' : ''}
                <button onclick="deleteTodo(${todo.id})" class="delete-btn">×</button>
            </li>
        `).join('');
    }

    // Initial render
    renderTodos();
    updatePendingCount();
</script>

<style>
    .todo-app {
        max-width: 600px;
        margin: 0 auto;
        padding: 20px;
    }

    .app-header {
        display: flex;
        justify-content: space-between;
        align-items: center;
        padding: 20px;
        border-radius: 8px;
        margin-bottom: 20px;
    }

    .sync-status {
        display: flex;
        align-items: center;
        gap: 8px;
        font-weight: 500;
    }

    .status-icon {
        font-size: 20px;
        animation: pulse 2s infinite;
    }

    .offline-notice {
        padding: 15px;
        background: #fef3c7;
        border-left: 4px solid #f59e0b;
        border-radius: 6px;
        margin-bottom: 20px;
    }

    .pending-sync {
        padding: 10px;
        background: #fef3c7;
        border-radius: 6px;
        margin-bottom: 15px;
        text-align: center;
        font-weight: 500;
    }

    #todo-form {
        display: flex;
        gap: 10px;
        margin-bottom: 20px;
    }

    #todo-input {
        flex: 1;
        padding: 10px;
        border: 1px solid #e5e7eb;
        border-radius: 6px;
        font-size: 16px;
    }

    #todo-form button {
        padding: 10px 20px;
        background: #3b82f6;
        color: white;
        border: none;
        border-radius: 6px;
        cursor: pointer;
        font-weight: 500;
    }

    #todo-list {
        list-style: none;
        padding: 0;
    }

    .todo-item {
        display: flex;
        align-items: center;
        gap: 10px;
        padding: 12px;
        background: white;
        border: 1px solid #e5e7eb;
        border-radius: 6px;
        margin-bottom: 8px;
    }

    .todo-item.completed .todo-text {
        text-decoration: line-through;
        color: #9ca3af;
    }

    .todo-text {
        flex: 1;
    }

    .sync-badge {
        padding: 4px 8px;
        background: #fef3c7;
        color: #92400e;
        border-radius: 4px;
        font-size: 12px;
        font-weight: 500;
    }

    .delete-btn {
        width: 24px;
        height: 24px;
        border: none;
        background: #ef4444;
        color: white;
        border-radius: 4px;
        cursor: pointer;
        font-size: 18px;
        line-height: 1;
    }

    @keyframes pulse {
        0%, 100% {
            opacity: 1;
        }
        50% {
            opacity: 0.5;
        }
    }
</style>

Troubleshooting

Status not updating

Issue: Connection status doesn't change when network connectivity changes

Solutions:

  • Ensure the controller is properly initialized

  • Check browser console for JavaScript errors

  • Verify that event listeners are attached correctly

  • Test with browser DevTools network throttling

False positives

Issue: Shows "online" even when internet is not accessible

Cause: navigator.onLine only checks browser's network connection, not actual internet access

Solution: Implement additional checks:

async function checkRealConnectivity() {
    try {
        const response = await fetch('/ping', {
            method: 'HEAD',
            cache: 'no-cache'
        });
        return response.ok;
    } catch {
        return false;
    }
}

Message not displaying

Issue: Connection status message doesn't appear

Solutions:

  • Verify the message target is properly set

  • Check that parameters onlineMessage and offlineMessage are configured

  • Inspect the element to ensure it's receiving content

Styling not applying

Issue: CSS classes based on data-connection-status not working

Solutions:

  • Ensure the attribute target is set on the correct element

  • Check CSS selector specificity

  • Verify Tailwind variants are configured if using Tailwind CSS

  • Use browser inspector to confirm the attribute is being set

Browser Compatibility

Browser
Support

Chrome

✓ Full support

Firefox

✓ Full support

Safari

✓ Full support

Edge

✓ Full support

Opera

✓ Full support

Mobile browsers

✓ Full support

The Connection Status component works reliably across all modern browsers and is based on well-established web platform APIs.

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