Why Deno's HTTP server uses web standards - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the HTTP server from Deno's standard library.

Deno

import { serve } from "https://deno.land/std/http/[1].ts";

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

Aserver

Bserver_mod

Dhttp_server

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect module names like 'server_mod' or 'http_server'.

Forgetting the '.ts' extension.

The correct module to import the HTTP server is 'server' from Deno's standard library.

2fill in blank

medium

Complete the code to create a basic HTTP server that responds with 'Hello World'.

Deno

serve((req) => new Response("Hello World"), { port: [1] });

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

A8080

B5000

C80

D3000

Attempts:

3 left

💡 Hint

Common Mistakes

Using port 80 without proper permissions.

Choosing ports not typically used for HTTP.

Port 8080 is commonly used for HTTP servers in development.

3fill in blank

hard

Fix the error in the code to correctly handle the request using web standards.

Deno

serve(async ([1]) => {
  const url = new URL(req.url);
  return new Response(`Path: ${url.pathname}`);
});

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

Aresponse

Breq

Cevent

Drequest

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different parameter name than the one referenced inside the function.

Confusing request and response objects.

The parameter name must match the variable used inside the function, which is 'req'.

4fill in blank

hard

Fill both blanks to create a response with a JSON body and correct headers.

Deno

serve((req) => {
  const data = { message: "Hello" };
  return new Response(JSON.stringify(data), { headers: { '[1]': '[2]' } });
});

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

AContent-Type

Bapplication/json

CAccept

Dtext/plain

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Accept' header instead of 'Content-Type'.

Setting content type to 'text/plain' for JSON data.

The header 'Content-Type' must be set to 'application/json' to indicate JSON response.

5fill in blank

hard

Fill all three blanks to correctly parse JSON from a POST request and respond with a message.

Deno

serve(async (req) => {
  if (req.method === '[1]') {
    const body = await req.json();
    const name = body.[2] || 'Guest';
    return new Response(`Hello, ${name}!`, { status: [3] });
  }
  return new Response('Method Not Allowed', { status: 405 });
});

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

APOST

Bname

C200

DGET

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for GET instead of POST.

Using wrong JSON key.

Returning wrong status code.

The server checks for POST method, extracts 'name' from JSON body, and responds with status 200.

Practice

1. Why does Deno's HTTP server use web standards like the Fetch API?

easy

A. To make server code familiar and easier to share with client code

B. To force developers to learn a new, unique API only for Deno

C. To improve server speed by using non-standard protocols

D. To prevent compatibility with browsers and other runtimes

Solution

1. Step 1: Understand the use of web standards in Deno

   Deno uses web standards like the Fetch API so developers can write code that feels familiar from the browser environment.

2. Step 2: Recognize the benefit of sharing code

   Using the same APIs on server and client makes sharing code easier and reduces bugs caused by different APIs.

3. Final Answer:

   To make server code familiar and easier to share with client code -> Option A

4. Quick Check:

   Web standards = Familiarity + Sharing [OK]

Hint: Web standards mean same code works client and server [OK]

Common Mistakes:

• Thinking Deno uses unique APIs only
• Believing web standards slow down the server
• Assuming web standards prevent browser compatibility

2. Which of the following is the correct way to create a basic HTTP server in Deno using web standards?

easy

A. import { createServer } from "deno_http";
createServer((req, res) => res.end("Hello"));

B. import http from "deno_http";
http.createServer((req, res) => res.send("Hello"));

C. import { serve } from "https://deno.land/std/http/server.ts";
serve(() => new Response("Hello"));

D. import { listenAndServe } from "deno_std";
listenAndServe((req) => "Hello");

Solution

1. Step 1: Identify the official Deno HTTP server import

   Deno's standard library provides the 'serve' function from "https://deno.land/std/http/server.ts" which uses web standards.

2. Step 2: Check the server creation syntax

   The correct syntax is calling serve with a handler function returning a Response object, matching web standards.

3. Final Answer:

   import { serve } from "https://deno.land/std/http/server.ts"; serve(() => new Response("Hello")); -> Option C

4. Quick Check:

   Use 'serve' + Response for Deno HTTP server [OK]

Hint: Use 'serve' from Deno std with Response object [OK]

Common Mistakes:

• Using Node.js style imports or APIs
• Calling res.end or res.send which are not web standard
• Importing from incorrect or non-existent modules

3. What will the following Deno HTTP server code output when accessed?

import { serve } from "https://deno.land/std/http/server.ts";
serve(req => {
  if (req.method === "POST") {
    return new Response("Posted!");
  }
  return new Response("Hello World");
});

medium

A. Always responds with "Posted!"

B. Responds with "Hello World" for GET and "Posted!" for POST

C. Throws an error because method check is invalid

D. Responds with "Hello World" for POST and "Posted!" for GET

Solution

1. Step 1: Analyze the request method check

   The code checks if the request method is "POST" and returns "Posted!" in that case.

2. Step 2: Understand the default response

   If the method is not "POST", it returns "Hello World". So GET requests get "Hello World".

3. Final Answer:

   Responds with "Hello World" for GET and "Posted!" for POST -> Option B

4. Quick Check:

   POST = "Posted!", others = "Hello World" [OK]

Hint: Check req.method to decide response text [OK]

Common Mistakes:

• Assuming all requests respond with "Posted!"
• Thinking method property is invalid or missing
• Mixing up POST and GET responses

4. Identify the error in this Deno HTTP server code snippet:

import { serve } from "https://deno.land/std/http/server.ts";
serve(req => {
  req.respond({ body: "Hello" });
});

medium

A. Using req.respond is incorrect; should return a Response object

B. Missing await keyword before req.respond

C. serve function is not imported correctly

D. Response body must be a Uint8Array, not a string

Solution

1. Step 1: Check the method used to send response

   The code calls req.respond, which is from older Deno APIs and not compatible with the web standard serve function.

2. Step 2: Understand the correct response pattern

   In the current Deno HTTP server, the handler must return a Response object instead of calling req.respond.

3. Final Answer:

   Using req.respond is incorrect; should return a Response object -> Option A

4. Quick Check:

   Return Response, don't call req.respond [OK]

Hint: Return Response object, don't call req.respond [OK]

Common Mistakes:

• Using old Deno APIs with new serve function
• Forgetting to return a Response
• Confusing async handling with req.respond

5. How does using web standards in Deno's HTTP server help reduce bugs when sharing code between client and server?

hard

A. Because web standards prevent any runtime errors

B. Because Deno automatically converts server code to client code

C. Because web standards force all code to be synchronous

D. Because both environments use the same APIs, reducing differences and surprises

Solution

1. Step 1: Understand the role of shared APIs

   Using the same web standard APIs on client and server means developers write similar code for both sides.

2. Step 2: Recognize how this reduces bugs

   When APIs match, fewer surprises happen due to different behaviors or missing features, reducing bugs.

3. Final Answer:

   Because both environments use the same APIs, reducing differences and surprises -> Option D

4. Quick Check:

   Same APIs = fewer bugs [OK]

Hint: Same APIs client/server means fewer bugs [OK]

Common Mistakes:

• Thinking Deno converts code automatically
• Believing web standards force sync code
• Assuming web standards eliminate all runtime errors