Routes and layouts in Deno - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a route in a web application?

A route is a path or URL that the app listens to and responds with specific content or a page. It connects a URL to code that shows what the user sees.

beginner

What is the purpose of a layout in web development?

A layout is a common structure or template used across multiple pages. It helps keep things like headers, footers, and navigation consistent.

intermediate

How do routes and layouts work together in a Deno web app?

Routes define what content to show for each URL, while layouts wrap that content with common page parts. Together, they build full pages with shared design.

intermediate

In Deno, how can you define a route that uses a layout?

You create a route handler that returns content wrapped inside a layout function or component. This way, the layout adds common parts around the route's unique content.

beginner

Why is using layouts beneficial when building multiple routes?

Layouts save time by reusing common page parts. They keep the look consistent and make it easier to update shared elements in one place instead of every page.

What does a route in a Deno web app represent?

A A URL path that shows specific content

B A style sheet for the page

C A database connection

D A user login form

Routes connect URL paths to the content or code that should run when that path is visited.

What is the main role of a layout in web development?

A To manage database queries

B To store user data

C To handle server requests

D To provide a common page structure

Layouts provide a shared structure like headers and footers for multiple pages.

How do layouts improve building multiple routes?

A By making each page load slower

B By reusing common page parts

C By repeating code on every page

D By removing navigation menus

Layouts let you reuse common parts, saving time and keeping pages consistent.

In Deno, what do you wrap route content with to apply a layout?

A A database query

B A CSS file

C A layout function or component

D A user session

You wrap route content inside a layout function or component to add shared page parts.

Which of these is NOT a benefit of using layouts?

A Slower page rendering

B Easier updates to shared parts

C Reusing code for common elements

D Consistent page design

Layouts improve efficiency and consistency; they do not slow down rendering.

Explain how routes and layouts work together in a Deno web application.

Think about how a page URL shows content inside a shared design.

Describe the benefits of using layouts when creating multiple routes.

Consider how changing one layout updates many pages.

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