Routes and layouts in Deno - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a route handler that responds with 'Hello World'.

Deno

import { serve } from "https://deno.land/std/http/server.ts";

serve((req) => {
  return new Response("[1]", { status: 200 });
});

Drag options to blanks, or click blank then click option'

Anew Response("Hello World")

BHello World

CResponse("Hello World")

D"Hello World"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the response text.

Passing a Response object inside another Response.

The Response constructor expects a string or body as the first argument. We pass the string "Hello World" to respond with that text.

2fill in blank

medium

Complete the code to import the Router from Oak framework.

Deno

import { [1] } from "https://deno.land/x/oak/mod.ts";

Drag options to blanks, or click blank then click option'

ARouter

BApplication

CContext

Dsend

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Application instead of Router.

Using Context which is for request context, not routing.

The Router is imported from Oak to define routes and layouts.

3fill in blank

hard

Fix the error in the route definition to respond with JSON data.

Deno

router.get('/data', (ctx) => {
  ctx.response.[1] = { message: 'Success' };
});

Drag options to blanks, or click blank then click option'

Atext

Bjson

Cbody

Dsend

Attempts:

3 left

💡 Hint

Common Mistakes

Using ctx.response.json which does not exist.

Trying to call a send method instead of setting body.

In Oak, to send JSON data, assign the object to ctx.response.body. Oak automatically sets the content type.

4fill in blank

hard

Fill both blanks to create a layout middleware that adds a header and footer around the content.

Deno

async function layout(ctx, next) {
  ctx.response.body = '<header>Header</header>' + [1];
  await next();
  ctx.response.body += [2];
}

Drag options to blanks, or click blank then click option'

Aawait next()

B'<footer>Footer</footer>'

C'<main>Content</main>'

Dctx.response.body

Attempts:

3 left

💡 Hint

Common Mistakes

Using await next() as a string instead of calling it.

Appending footer before calling next middleware.

We wrap the existing body content by first adding the header, then the existing body (ctx.response.body), then after next middleware, append the footer.

5fill in blank

hard

Fill all three blanks to define a route with a dynamic parameter and respond with it.

Deno

router.get('/user/[1]', (ctx) => {
  const id = ctx.params.[2];
  ctx.response.body = { userId: [3] };
});

Drag options to blanks, or click blank then click option'

A:id

Bid

DuserId

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the colon in the route parameter.

Using wrong property name in ctx.params.

Not returning the parameter value in response.

The route uses :id to capture the dynamic segment. We access it via ctx.params.id and respond with that value.

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