Why Deno's HTTP server uses web standards

Introduction

Deno's HTTP server uses web standards to make it easy and familiar for developers to build web apps. It helps code work smoothly across different platforms and tools.

When building a web server that should work like browsers expect

When you want your server code to be easy to understand and maintain

When you want to use modern web APIs on the server side

When you want your server to handle requests and responses in a standard way

When you want to share code between client and server easily

Syntax

Deno

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

serve((request) => {
  return new Response("Hello from Deno HTTP server!", {
    status: 200,
    headers: { "content-type": "text/plain" },
  });
});

The serve function takes a handler that receives a Request object and returns a Response object.

Both Request and Response follow the web standard Fetch API used in browsers.

Examples

Simple server that responds with plain text "Hello World" and status 200.

Deno

serve((request) => {
  return new Response("Hello World", { status: 200 });
});

Server that returns JSON on /json path and 404 for others.

Deno

serve((request) => {
  const url = new URL(request.url);
  if (url.pathname === "/json") {
    return new Response(JSON.stringify({ message: "Hello JSON" }), {
      headers: { "content-type": "application/json" },
    });
  }
  return new Response("Not Found", { status: 404 });
});

Sample Program

This program starts a simple HTTP server using Deno's web standard APIs. It responds with different messages based on the URL path.

Deno

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

console.log("HTTP web server running. Access it at: http://localhost:8000/");

serve((request) => {
  const url = new URL(request.url);
  if (url.pathname === "/") {
    return new Response("Welcome to Deno HTTP server using web standards!", {
      headers: { "content-type": "text/plain" },
    });
  } else if (url.pathname === "/hello") {
    return new Response("Hello there!", {
      headers: { "content-type": "text/plain" },
    });
  } else {
    return new Response("Page not found", { status: 404 });
  }
});

Important Notes

Using web standards means you can use the same Request and Response objects on both client and server.

This approach reduces confusion and helps reuse code between browser and server.

Deno's HTTP server is easy to learn if you already know how web browsers work.

Summary

Deno's HTTP server uses web standards to keep things simple and familiar.

This helps developers write code that works well across different environments.

It makes sharing code between client and server easier and reduces bugs.

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