Routes and layouts in Deno

Introduction

Routes help your app show different pages based on the URL. Layouts keep parts of the page the same, like a header or footer, so you don't repeat code.

You want to show a home page, about page, and contact page in your app.

You want a menu or header to appear on every page without rewriting it.

You want to organize your app so each URL shows different content.

You want to keep your page design consistent across many pages.

Syntax

Deno

import { Application, Router } from "https://deno.land/x/oak/mod.ts";

const router = new Router();

router.get("/", (context) => {
  context.response.body = renderLayout("Home", "Welcome to the home page!");
});

function renderLayout(title, content) {
  return `
    <html>
      <head><title>${title}</title></head>
      <body>
        <header><h1>My Site</h1></header>
        <main>${content}</main>
        <footer>© 2024 My Site</footer>
      </body>
    </html>
  `;
}

const app = new Application();
app.use(router.routes());
app.use(router.allowedMethods());

await app.listen({ port: 8000 });

Routes map URLs to functions that send back content.

Layouts are functions or templates that wrap your page content with common parts like header and footer.

Examples

This route shows the About page with the same layout.

Deno

router.get("/about", (ctx) => {
  ctx.response.body = renderLayout("About", "This is the about page.");
});

This layout adds a navigation menu to every page.

Deno

function renderLayout(title, content) {
  return `
    <html>
      <head><title>${title}</title></head>
      <body>
        <nav>Menu here</nav>
        <main>${content}</main>
        <footer>Footer here</footer>
      </body>
    </html>
  `;
}

Sample Program

This Deno app uses Oak to create two routes: home and about. Both use the same layout with header and footer. When you visit each URL, you see the page content inside the layout.

Deno

import { Application, Router } from "https://deno.land/x/oak/mod.ts";

const router = new Router();

function renderLayout(title, content) {
  return `
    <html lang="en">
      <head>
        <meta charset="UTF-8" />
        <meta name="viewport" content="width=device-width, initial-scale=1.0" />
        <title>${title}</title>
        <style>
          body { font-family: Arial, sans-serif; margin: 2rem; }
          header, footer { background: #eee; padding: 1rem; text-align: center; }
          main { margin: 2rem 0; }
        </style>
      </head>
      <body>
        <header><h1>My Deno Site</h1></header>
        <main>${content}</main>
        <footer>© 2024 My Deno Site</footer>
      </body>
    </html>
  `;
}

router.get("/", (ctx) => {
  ctx.response.body = renderLayout("Home", "<p>Welcome to the home page!</p>");
});

router.get("/about", (ctx) => {
  ctx.response.body = renderLayout("About", "<p>This is the about page.</p>");
});

const app = new Application();
app.use(router.routes());
app.use(router.allowedMethods());

console.log("Server running on http://localhost:8000");
await app.listen({ port: 8000 });

Important Notes

Always include lang and meta tags in your HTML for accessibility and responsiveness.

Layouts help keep your site consistent and easier to update.

Use semantic HTML tags like <header>, <main>, and <footer> for better structure and accessibility.

Summary

Routes connect URLs to content in your app.

Layouts wrap your content with common page parts like header and footer.

Using routes and layouts together keeps your app organized and easy to maintain.

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