Why Deno's HTTP server uses web standards - See It in Action

Why Deno's HTTP server uses web standards

📖 Scenario: You are learning how Deno's HTTP server works. Deno uses web standards like the Fetch API to handle requests and responses. This makes the server code familiar and easy to understand for anyone who knows web programming.

🎯 Goal: Build a simple HTTP server in Deno that uses the Fetch API to respond to requests. You will see how using web standards makes the server code clean and easy to read.

📋 What You'll Learn

Create a basic HTTP server using Deno's standard library

Use the Fetch API's Request and Response objects

Handle incoming requests and send back a simple text response

Use async functions and web standard patterns

💡 Why This Matters

🌍 Real World

Web servers built with Deno can use familiar web APIs, making it easier for web developers to write backend code without learning new server-specific APIs.

💼 Career

Understanding how Deno uses web standards prepares you for modern backend development and helps you write clean, maintainable server code that aligns with web platform conventions.

1

Set up a basic HTTP server with Deno

Write code to import the serve function from "https://deno.land/std@0.177.0/http/server.ts" and start a server on port 8000 using serve. Assign the server to a variable called server.

Deno

import { serve } from "https://deno.land/std@0.177.0/http/server.ts";

// Start the server on port 8000
// Your code here

Hint

Use import { serve } from "https://deno.land/std@0.177.0/http/server.ts" and then call serve with { port: 8000 }.

2

Create an async loop to handle requests

Add an async for await loop that iterates over server to handle incoming requests. Use the variable name requestEvent for each iteration.

Deno

import { serve } from "https://deno.land/std@0.177.0/http/server.ts";

const server = serve({ port: 8000 });

// Use an async for-await loop to handle requests
// Your code here

Hint

Use for await (const requestEvent of server) to handle each incoming request asynchronously.

3

Use web standard Request and Response objects

Inside the loop, get the request from requestEvent.request. Then create a new Response object with the text "Hello from Deno!" and assign it to a variable called response.

Deno

import { serve } from "https://deno.land/std@0.177.0/http/server.ts";

const server = serve({ port: 8000 });

for await (const requestEvent of server) {
  // Get the request object
  // Your code here

  // Create a Response with text
  // Your code here
}

Hint

Use const request = requestEvent.request and then const response = new Response("Hello from Deno!").

4

Send the response using web standards

Call requestEvent.respondWith(response) inside the loop to send the response back to the client.

Deno

import { serve } from "https://deno.land/std@0.177.0/http/server.ts";

const server = serve({ port: 8000 });

for await (const requestEvent of server) {
  const request = requestEvent.request;
  const response = new Response("Hello from Deno!");

  // Send the response
  // Your code here
}

Hint

Use requestEvent.respondWith(response) to send the response.

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