Step 4: Building a Multi-Page App

Let's bring it all together! In this step, we'll complete the index → login → welcome flow that every real app needs. You'll see exactly how data flows between pages.

The Complete App Structure

By the end of this page, you'll have:

src/blocks/
├── home-page.lego      ← Landing page (/)
├── login-page.lego     ← Login form (/login)
└── welcome-page.lego   ← Dashboard (/welcome)

Step 1: Create the Welcome Page

Create src/blocks/welcome-page.lego:

html

<template>
  <div class="dashboard">
    <header>
      <h1>Welcome, [[ username ]]! 🎉</h1>
      <button @click="handleLogout()">Logout</button>
    </header>
    
    <main>
      <div class="card">
        <h2>You're In!</h2>
        <p>You've successfully navigated through a complete authentication flow built with LegoDOM.</p>
        <p>This page received your username from the login form using global state.</p>
      </div>
      
      <div class="stats">
        <div class="stat">
          <span class="value">[[ visitCount ]]</span>
          <span class="label">Page Views</span>
        </div>
        <div class="stat">
          <span class="value">[[ formatTime() ]]</span>
          <span class="label">Current Time</span>
        </div>
        <div class="stat">
          <span class="value">✓</span>
          <span class="label">Logged In</span>
        </div>
      </div>
      
      <div class="actions">
        <a href="/" b-link class="btn">← Back to Home</a>
      </div>
    </main>
  </div>
</template>

<style>
  self {
    display: block;
    min-height: 100vh;
    background: linear-gradient(180deg, #1a1a2e 0%, #16213e 100%);
    color: white;
    padding: 2rem;
  }
  
  header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    max-width: 800px;
    margin: 0 auto 3rem;
  }
  
  header h1 {
    font-size: 1.75rem;
  }
  
  header button {
    background: rgba(255,255,255,0.1);
    color: white;
    border: 1px solid rgba(255,255,255,0.2);
    padding: 0.5rem 1rem;
    border-radius: 6px;
    cursor: pointer;
    transition: background 0.2s;
  }
  
  header button:hover {
    background: rgba(255,255,255,0.2);
  }
  
  main {
    max-width: 800px;
    margin: 0 auto;
  }
  
  .card {
    background: rgba(255,255,255,0.05);
    padding: 2rem;
    border-radius: 16px;
    margin-bottom: 2rem;
    border: 1px solid rgba(255,255,255,0.1);
  }
  
  .card h2 {
    color: #4ecca3;
    margin-bottom: 1rem;
  }
  
  .card p {
    opacity: 0.8;
    line-height: 1.6;
    margin-bottom: 0.5rem;
  }
  
  .stats {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 1rem;
    margin-bottom: 2rem;
  }
  
  .stat {
    background: rgba(255,255,255,0.05);
    padding: 1.5rem;
    border-radius: 12px;
    text-align: center;
    border: 1px solid rgba(255,255,255,0.1);
  }
  
  .stat .value {
    display: block;
    font-size: 2rem;
    font-weight: bold;
    color: #4ecca3;
    margin-bottom: 0.5rem;
  }
  
  .stat .label {
    font-size: 0.85rem;
    opacity: 0.7;
  }
  
  .actions {
    text-align: center;
  }
  
  .btn {
    display: inline-block;
    padding: 0.75rem 1.5rem;
    background: #4ecca3;
    color: #1a1a2e;
    text-decoration: none;
    border-radius: 8px;
    font-weight: 600;
  }
</style>

<script>
export default {
  visitCount: 0,
  
  get username() {
    // Get username from global state (set by login page)
    return Lego.globals.user?.name || 'Guest';
  },
  
  mounted() {
    this.visitCount++;
    
    // Redirect to login if not authenticated
    if (!Lego.globals.user) {
      console.log('Not logged in, redirecting...');
      this.$go('/login').get();
    }
  },
  
  formatTime() {
    return new Date().toLocaleTimeString();
  },
  
  handleLogout() {
    // Clear global user state
    Lego.globals.user = null;
    this.$go('/').get();
  }
}
</script>

The login page needs to store the user in global state. Update src/blocks/login-page.lego's script section:

javascript

<script>
export default {
  email: '',
  password: '',
  
  handleSubmit(event) {
    event.preventDefault();
    
    // Store user in GLOBAL state (accessible from any block!)
    Lego.globals.user = {
      name: this.email.split('@')[0],  // Use email prefix as name
      email: this.email,
      loggedInAt: new Date()
    };
    
    console.log('User logged in:', Lego.globals.user);
    
    // Navigate to welcome page
    this.$go('/welcome').get();
  }
}
</script>

Update src/blocks/home-page.lego's handleClick method:

javascript

handleClick() {
  this.$go('/login').get();
}

Step 4: Complete `app.js`

Here's the final src/app.js:

javascript

import { Lego } from 'lego-dom';
import registerBlocks from 'virtual:lego-blocks';

// Register all .lego blocks
registerBlocks();

// Define routes
Lego.route('/', 'home-page');
Lego.route('/login', 'login-page');
Lego.route('/welcome', 'welcome-page');

// Initialize with default user state
Lego.globals.user = null;

// Start the engine
await Lego.init();

Test the Complete Flow

bash

npm run dev

Home Page (/) – Click "Get Started"
Login Page (/login) – Enter an email, click "Sign In"
Welcome Page (/welcome) – See your username displayed!
Click "Logout" – Clears state, returns to home
Try navigating directly to /welcome – Redirects to login!

The Data Flow

┌─────────────────────────────────────────────────────────────┐
│                        Lego.globals                          │
│  ┌─────────────────────────────────────────────────────┐    │
│  │  user: { name: 'john', email: 'john@test.com' }    │    │
│  └─────────────────────────────────────────────────────┘    │
└─────────────────────────────────────────────────────────────┘
         ▲                                    │
         │ writes                             │ reads
         │                                    ▼
   ┌──────────┐                        ┌──────────────┐
   │  login   │                        │   welcome    │
   │  page    │                        │    page      │
   └──────────┘                        └──────────────┘

Auth Guard Pattern

Want to protect routes? Add middleware:

javascript

// In app.js

const requireAuth = (params, globals) => {
  if (!globals.user) {
    globals.$go('/login').get();
    return false;  // Block navigation
  }
  return true;  // Allow navigation
};

Lego.route('/welcome', 'welcome-page', requireAuth);
Lego.route('/dashboard', 'dashboard-page', requireAuth);
Lego.route('/settings', 'settings-page', requireAuth);

What You've Built

✅ A complete login flow: home → login → welcome
✅ Global state shared across blocks
✅ Logout functionality that clears state
✅ Automatic redirect when not authenticated
✅ Route protection with middleware

The Full Picture

File	Purpose
`index.html`	Entry HTML with `<lego-router>`
`src/app.js`	Routes, globals, initialization
`src/blocks/*.lego`	Your page blocks
`vite.config.js`	Vite + LegoDOM plugin setup

← Previous: Adding Routes Next: State & Globals →

Step 4: Building a Multi-Page App ​

The Complete App Structure ​

Step 1: Create the Welcome Page ​

Step 2: Update Login to Set Global State ​

Step 3: Update Home Page Navigation ​

Step 4: Complete app.js ​

Test the Complete Flow ​

The Data Flow ​

Auth Guard Pattern ​

What You've Built ​

The Full Picture ​

Step 4: Building a Multi-Page App

The Complete App Structure

Step 1: Create the Welcome Page

Step 2: Update Login to Set Global State

Step 3: Update Home Page Navigation

Step 4: Complete `app.js`

Test the Complete Flow

The Data Flow

Auth Guard Pattern

What You've Built

The Full Picture