Routes and layouts in Deno - Mini Project: Build & Apply

Building Routes and Layouts in Deno Fresh

📖 Scenario: You are creating a simple website using Deno Fresh framework. The website will have multiple pages with a shared layout that includes a header and footer.

🎯 Goal: Build a Deno Fresh project with two routes: a home page and an about page. Both pages should use a shared layout component that displays a header and footer.

📋 What You'll Learn

Create a route file for the home page at routes/index.tsx with a simple welcome message.

Create a route file for the about page at routes/about.tsx with an about message.

Create a shared layout component in components/Layout.tsx that includes a header and footer.

Use the shared layout component in both route files to wrap their content.

💡 Why This Matters

🌍 Real World

Websites often have multiple pages sharing common headers, footers, or sidebars. Using layouts helps keep the design consistent and code organized.

💼 Career

Understanding routing and layouts is essential for frontend developers working with modern frameworks like Deno Fresh, Next.js, or React Router.

1

Create the home page route

Create a file routes/index.tsx with a default exported function component called HomePage that returns a <main> element containing the text "Welcome to the Home Page".

Deno

// Your code here

Hint

Use a React-style function component that returns JSX with a <main> tag and the exact text.

2

Create the about page route

Create a file routes/about.tsx with a default exported function component called AboutPage that returns a <main> element containing the text "About Us".

Deno

export default function HomePage() {
  return Welcome to the Home Page;
}

// Your code here

Hint

Create a new function component named AboutPage that returns a <main> tag with the exact text.

3

Create the shared layout component

Create a file components/Layout.tsx with a default exported function component called Layout that accepts a children prop and returns a <div> containing a <header> with text "Site Header", the children, and a <footer> with text "Site Footer".

Deno

export default function HomePage() {
  return Welcome to the Home Page;
}

export default function AboutPage() {
  return About Us;
}

// Your code here

Hint

Use a function component with a children prop and wrap it between header and footer elements.

4

Use the layout component in routes

Modify routes/index.tsx and routes/about.tsx to import the Layout component from components/Layout.tsx and wrap their returned <main> content inside <Layout> tags.

Deno

import Layout from "../components/Layout.tsx";

export default function HomePage() {
  // Your code here
}

import Layout from "../components/Layout.tsx";

export default function AboutPage() {
  // Your code here
}

import { ReactNode } from "https://esm.sh/react";

export default function Layout({ children }: { children: ReactNode }) {
  return (
    
      Site Header
      {children}
      Site Footer
    
  );
}

Hint

Import Layout and wrap the <main> content inside <Layout> tags in both route components.

Practice

1. What is the main purpose of routes in a Deno web application?

easy

A. To store user data in a database

B. To style the application with CSS

C. To connect URLs to specific content or pages

D. To handle server hardware settings

Solution

1. Step 1: Understand what routes do

   Routes link a URL path to the content or page that should show when that URL is visited.

2. Step 2: Compare options to this definition

   Only To connect URLs to specific content or pages describes connecting URLs to content, which matches the purpose of routes.

3. Final Answer:

   To connect URLs to specific content or pages -> Option C

4. Quick Check:

   Routes = URL to content connection [OK]

Hint: Routes map URLs to pages or content [OK]

Common Mistakes:

• Confusing routes with styling or database tasks
• Thinking routes manage server hardware
• Mixing routes with layout responsibilities

2. Which of the following is the correct way to define a route handler in a Deno Oak application?

easy

A. router.route('/home', function() { return 'Home'; });

B. router.get('/home', (ctx) => { ctx.response.body = 'Home'; });

C. router.add('/home', (req, res) => res.send('Home'));

D. router.handle('/home', () => { print('Home'); });

Solution

1. Step 1: Recall Oak router syntax

   In Oak, routes are defined using methods like router.get(path, handler).

2. Step 2: Check each option's syntax

   router.get('/home', (ctx) => { ctx.response.body = 'Home'; }); uses router.get with a context parameter and sets ctx.response.body, which is correct Oak syntax.

3. Final Answer:

   router.get('/home', (ctx) => { ctx.response.body = 'Home'; }); -> Option B

4. Quick Check:

   Oak route syntax = router.get(path, ctx) [OK]

Hint: Use router.get with ctx and set ctx.response.body [OK]

Common Mistakes:

• Using non-existent router methods like add or handle
• Not setting ctx.response.body for response
• Confusing callback parameters with Express.js style

3. Given this Deno Oak route and layout setup, what will be the output when visiting '/about'?

const router = new Router();
router.get('/about', (ctx) => { ctx.response.body = 'About Page'; });

const layout = (content) => `
Header
${content}
Footer
`;

// Middleware to wrap response
app.use(async (ctx, next) => {
  await next();
  ctx.response.body = layout(ctx.response.body);
});

app.use(router.routes());
app.use(router.allowedMethods());

medium

A. HeaderAbout PageFooter

B. About Page

C. HeaderFooter

D. Error: layout function not applied

Solution

1. Step 1: Understand route response

   The route sets ctx.response.body to 'About Page' when '/about' is visited.

2. Step 2: Understand middleware wrapping

   The middleware runs after the route, wrapping the body with header and footer HTML using the layout function.

3. Final Answer:

   <header>Header</header>About Page<footer>Footer</footer> -> Option A

4. Quick Check:

   Middleware wraps route output with layout [OK]

Hint: Middleware modifies response after route sets it [OK]

Common Mistakes:

• Ignoring middleware wrapping
• Assuming route output is unchanged
• Confusing order of middleware and routes

4. Identify the error in this Deno Oak route and layout code snippet:

const router = new Router();
router.get('/contact', (ctx) => {
  ctx.response.body = 'Contact Page';
});

const layout = (content) => `
Header
${content}
Footer
`;

app.use(router.routes());
app.use(router.allowedMethods());

app.use(async (ctx, next) => {
  await next();
  ctx.response.body = layout(ctx.response.body);
});

medium

A. router.allowedMethods() is missing

B. Middleware wrapping layout runs after routes, so layout is applied too late

C. ctx.response.body is not set in route handler

D. Middleware wrapping layout runs after routes, so layout is not applied

Solution

1. Step 1: Analyze middleware order

   router.routes() and router.allowedMethods() are registered before the layout middleware.

2. Step 2: Recall route handler behavior in Oak

   When router.routes() matches a route, it executes the handler. The handler sets the response body but does not call next(), terminating the middleware chain at that point.

3. Step 3: Determine layout application

   Subsequent middleware, including the layout wrapper, are never reached for matched routes. Thus, the layout is not applied.

4. Final Answer:

   Middleware wrapping layout runs after routes, so layout is not applied -> Option D

5. Quick Check:

   Middleware after router.routes() skipped on match [OK]

Hint: Layout middleware must precede router.routes() [OK]

Common Mistakes:

• Placing layout middleware after routes
• Forgetting to set ctx.response.body in route
• Misunderstanding middleware execution order

5. You want to create a Deno Oak app with a layout that adds a header and footer to all pages, but only for routes under '/app'. Which approach correctly applies the layout only to those routes?

hard

A. Use a middleware that checks if ctx.request.url.pathname starts with '/app' and wraps response body with layout only then

B. Apply the layout middleware globally to all routes without condition

C. Add the header and footer HTML directly inside each route handler under '/app'

D. Use router.allowedMethods() to apply layout only to '/app' routes

Solution

1. Step 1: Understand the requirement

   The layout should wrap only routes under '/app', not all routes.

2. Step 2: Evaluate each option

   Use a middleware that checks if ctx.request.url.pathname starts with '/app' and wraps response body with layout only then uses middleware that checks the URL path and applies layout conditionally, which is correct and efficient.

3. Step 3: Why other options fail

   Apply the layout middleware globally to all routes without condition applies layout to all routes, ignoring the condition. Add the header and footer HTML directly inside each route handler under '/app' duplicates layout code in every route, which is not DRY. Use router.allowedMethods() to apply layout only to '/app' routes misuses router.allowedMethods(), which only handles HTTP method responses.

4. Final Answer:

   Use a middleware that checks if ctx.request.url.pathname starts with '/app' and wraps response body with layout only then -> Option A

5. Quick Check:

   Conditional middleware applies layout selectively [OK]

Hint: Check URL path in middleware to apply layout selectively [OK]

Common Mistakes:

• Applying layout middleware globally without condition
• Repeating layout code in each route
• Misusing router.allowedMethods() for layout