Serving static files in Deno - Mini Project: Build & Apply

Serving Static Files with Deno

📖 Scenario: You want to create a simple web server using Deno that can serve static files like HTML, CSS, and images from a folder called public. This is useful when you want to share a website or assets without complex backend logic.

🎯 Goal: Build a Deno server that listens on port 8000 and serves files from the public directory. When a user visits http://localhost:8000/index.html, the server should return the index.html file from the public folder.

📋 What You'll Learn

Create a basic HTTP server using Deno's standard library

Set the server to listen on port 8000

Serve files from a folder named public

Return a 404 response if the requested file does not exist

💡 Why This Matters

🌍 Real World

Serving static files is a common need for hosting websites, assets, or documentation without complex backend logic.

💼 Career

Understanding how to serve static files is essential for web developers and backend engineers working with web servers and deployment.

1

Create the HTTP server

Import serve from https://deno.land/std@0.203.0/http/server.ts and create a server that listens on port 8000. Assign the server to a variable called server.

Deno

import { serve } from "https://deno.land/std@0.203.0/http/server.ts";

// Create the server listening on port 8000
// Your code here

Hint

Use serve with an object specifying port: 8000.

2

Set up the public directory path

Create a constant called publicDir and set it to the string "./public" which will be the folder where static files are stored.

Deno

import { serve } from "https://deno.land/std@0.203.0/http/server.ts";

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

// Define the public directory path
// Your code here

Hint

Use a string with the relative path "./public".

3

Serve static files on requests

Write an async for await loop over server. Inside the loop, get the requested URL path from req.url. Use new URL(req.url, `http://localhost`) to parse the path. Then create a file path by joining publicDir and the URL pathname. Use Deno.readFile to read the file. If the file exists, respond with status 200 and the file content. If it does not exist, respond with status 404 and a plain text message "File not found".

Deno

import { serve } from "https://deno.land/std@0.203.0/http/server.ts";

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

const publicDir = "./public";

// Start serving files
// Your code here

Hint

Use a for await loop and try/catch to handle file reading.

4

Add content-type header for HTML files

Modify the response for successful file reads to include a Content-Type header with value text/html if the requested file ends with .html. Add a variable headers that sets this header conditionally, and include it in the req.respond call.

Deno

import { serve } from "https://deno.land/std@0.203.0/http/server.ts";

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

const publicDir = "./public";

for await (const req of server) {
  const url = new URL(req.url, `http://localhost`);
  const filepath = `${publicDir}${url.pathname}`;
  try {
    const file = await Deno.readFile(filepath);
    // Add content-type header for .html files
    // Your code here
  } catch {
    req.respond({ status: 404, body: "File not found" });
  }
}

Hint

Use url.pathname.endsWith('.html') to check the file extension and set headers accordingly.

Practice

1. What is the main purpose of serving static files in a Deno web server?

easy

A. To send images, styles, and scripts to the user's browser

B. To execute server-side scripts dynamically

C. To connect to a database and fetch data

D. To compile TypeScript files on the server

Solution

1. Step 1: Understand what static files are

   Static files include images, CSS stylesheets, and JavaScript files that do not change dynamically.

2. Step 2: Identify the purpose of serving static files

   Serving static files means sending these files from the server to the user's browser so the webpage looks and works correctly.

3. Final Answer:

   To send images, styles, and scripts to the user's browser -> Option A

4. Quick Check:

   Static files = images, styles, scripts [OK]

Hint: Static files are fixed resources sent to browsers [OK]

Common Mistakes:

• Confusing static files with dynamic server code
• Thinking static files run on the server
• Mixing static files with database operations

2. Which of the following is the correct way to import the function to serve static files in Deno?

easy

A. import { serveFile } from "https://deno.land/std/fs/mod.ts";

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

C. import { serveFile } from "https://deno.land/std/http/file.ts";

D. import { serveFile } from "https://deno.land/std/http/file_server.ts";

Solution

1. Step 1: Identify the correct module for serving static files

   The function serveFile is provided by the file.ts module in Deno's standard HTTP library.

2. Step 2: Match the import path

   The correct import path is "https://deno.land/std/http/file.ts" for serveFile.

3. Final Answer:

   import { serveFile } from "https://deno.land/std/http/file.ts"; -> Option C

4. Quick Check:

   serveFile import = file.ts [OK]

Hint: serveFile comes from file.ts in std/http [OK]

Common Mistakes:

• Using server.ts instead of file.ts
• Importing from fs module incorrectly
• Wrong URL path for the import

3. Given this Deno server code snippet, what will be the response when a user requests /image.png?

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

serve(async (req) => {
  const url = new URL(req.url);
  if (url.pathname === "/image.png") {
    return await serveFile(req, "./static/image.png");
  }
  return new Response("Not Found", { status: 404 });
});

medium

A. The server throws a runtime error because serveFile is used incorrectly

B. The server sends the file located at ./static/image.png to the user

C. The server returns a 404 Not Found response

D. The server sends an empty response with status 200

Solution

1. Step 1: Check the URL path condition

   The code checks if the requested path is exactly "/image.png".

2. Step 2: Understand serveFile usage

   If the path matches, serveFile sends the file "./static/image.png" as the response.

3. Final Answer:

   The server sends the file located at ./static/image.png to the user -> Option B

4. Quick Check:

   Path matches "/image.png" so serveFile sends file [OK]

Hint: Check URL path then serveFile sends matching file [OK]

Common Mistakes:

• Assuming 404 is returned for existing path
• Thinking serveFile causes error here
• Ignoring the URL pathname check

4. Identify the error in this Deno code snippet for serving a static CSS file:

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

serve(async (req) => {
  const url = new URL(req.url);
  if (url.pathname = "/style.css") {
    return await serveFile(req, "./static/style.css");
  }
  return new Response("Not Found", { status: 404 });
});

medium

A. The server function is not awaited

B. serveFile is missing an await keyword

C. The import path for serveFile is incorrect

D. The assignment operator (=) is used instead of comparison (===) in the if condition

Solution

1. Step 1: Check the if condition syntax

   The condition uses a single equals sign (=), which assigns instead of compares.

2. Step 2: Understand the impact of assignment in if

   Using = in if always evaluates to true, causing incorrect logic and possible bugs.

3. Final Answer:

   The assignment operator (=) is used instead of comparison (===) in the if condition -> Option D

4. Quick Check:

   Use === for comparison, not = [OK]

Hint: Use === for comparison, not = assignment in conditions [OK]

Common Mistakes:

• Confusing = with === in if statements
• Forgetting to await serveFile (though it is awaited here)
• Incorrect import paths

5. You want to serve multiple static files (HTML, CSS, JS) from a folder named public in Deno. Which approach correctly serves any requested file from that folder, falling back to a 404 if the file doesn't exist?

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

serve(async (req) => {
  const url = new URL(req.url);
  try {
    // Which line correctly serves the file?
    return await ???;
  } catch {
    return new Response("Not Found", { status: 404 });
  }
});

hard

A. serveFile(req, `./public${url.pathname}`)

B. serveFile(req, `./public/index.html`)

C. serveFile(req, `./public/style.css`)

D. serveFile(req, `./public/${url.searchParams.get('file')}`)

Solution

1. Step 1: Understand dynamic file serving

   To serve any file requested, the server must use the URL path to build the file path inside the public folder.

2. Step 2: Match the URL pathname to the file path

   Using `./public${url.pathname}` correctly maps the request path to the file location.

3. Final Answer:

   serveFile(req, `./public${url.pathname}`) -> Option A

4. Quick Check:

   Dynamic path = ./public + url.pathname [OK]

Hint: Use url.pathname appended to folder path for dynamic files [OK]

Common Mistakes:

• Serving only a fixed file like index.html
• Using query parameters instead of pathname
• Hardcoding a single file path