Serving from multiple directories in Express - Mini Project: Build & Apply

Serving Static Files from Multiple Directories in Express

📖 Scenario: You are building a simple web server using Express.js. You want to serve static files like images, CSS, and JavaScript from two different folders: public and assets. This way, your website can load files from both places seamlessly.

🎯 Goal: Build an Express server that serves static files from two directories: public and assets. When a user visits your site, files from both folders should be accessible.

📋 What You'll Learn

Create an Express app instance

Serve static files from the public directory

Serve static files from the assets directory

Listen on port 3000

💡 Why This Matters

🌍 Real World

Web servers often need to serve static files like images, stylesheets, and scripts from multiple folders. This project shows how to do that with Express.

💼 Career

Knowing how to serve static assets from multiple directories is a common task for backend developers working with Node.js and Express.

1

Create the Express app

Write code to import express and create an Express app instance called app.

Express

# Import express and create app
# Your code here

Hint

Use import express from 'express' and then const app = express().

2

Serve static files from the public directory

Add code to serve static files from the public directory using app.use(express.static('public')).

Express

import express from 'express';
const app = express();

# Serve static files from 'public' directory
# Your code here

Hint

Use app.use(express.static('public')) to serve files from the public folder.

3

Serve static files from the assets directory

Add code to serve static files from the assets directory using app.use(express.static('assets')).

Express

import express from 'express';
const app = express();

app.use(express.static('public'));

# Serve static files from 'assets' directory
# Your code here

Hint

Use app.use(express.static('assets')) to serve files from the assets folder.

4

Start the server on port 3000

Add code to make the app listen on port 3000 using app.listen(3000).

Express

import express from 'express';
const app = express();

app.use(express.static('public'));
app.use(express.static('assets'));

# Start server on port 3000
# Your code here

Hint

Use app.listen(3000) to start the server on port 3000.

Practice

1. What happens when you use multiple app.use(express.static()) calls with different directories in Express?

easy

A. Express throws an error if multiple static directories are used.

B. Express merges all directories into one and serves files randomly from any directory.

C. Express only serves files from the last directory added with express.static().

D. Express serves static files by checking each directory in the order they were added until it finds the file.

Solution

1. Step 1: Understand how Express static middleware works

   Each app.use(express.static()) adds a middleware that checks its directory for requested files.

2. Step 2: Order of middleware matters

   Express checks these middlewares in the order they were added and serves the first matching file it finds.

3. Final Answer:

   Express serves static files by checking each directory in the order they were added until it finds the file. -> Option D

4. Quick Check:

   Multiple static folders checked in order = D [OK]

Hint: Remember: Express checks static folders in order added [OK]

Common Mistakes:

• Thinking Express merges directories randomly
• Believing only the last directory is used
• Assuming multiple static folders cause errors

2. Which of the following is the correct way to serve static files from two directories named public and assets in Express?

easy

A. app.use(express.static('public')); app.use(express.static('assets'));

B. app.use(express.static(['public', 'assets']));

C. app.use(express.static('public', 'assets'));

D. app.use(express.static('public')); app.use.static('assets');

Solution

1. Step 1: Check Express static syntax

   The express.static() middleware accepts only one directory path at a time.

2. Step 2: Use multiple app.use() calls

   To serve multiple directories, call app.use(express.static()) separately for each directory.

3. Final Answer:

   app.use(express.static('public')); app.use(express.static('assets')); -> Option A

4. Quick Check:

   Multiple static folders need separate app.use calls = C [OK]

Hint: Use separate app.use calls for each static folder [OK]

Common Mistakes:

• Passing multiple directories in one express.static call
• Using incorrect method like app.use.static
• Passing an array instead of separate calls

3. Given the code below, what file will Express serve when a user requests /image.png? Assume both directories contain a file named image.png.

app.use(express.static('public'));
app.use(express.static('assets'));

medium

A. The image.png from the public directory.

B. The image.png from the assets directory.

C. An error because the file exists in both directories.

D. No file will be served; Express will return 404.

Solution

1. Step 1: Understand middleware order

   Express checks static directories in the order they are added. Here, public is checked first.

2. Step 2: First match is served

   Since image.png exists in public, Express serves that file and stops checking further.

3. Final Answer:

   The image.png from the public directory. -> Option A

4. Quick Check:

   First matching static file served = A [OK]

Hint: Express serves first found file in order of static folders [OK]

Common Mistakes:

• Assuming Express merges files from both directories
• Thinking Express throws error on duplicates
• Believing the last directory has priority

4. Identify the error in the following Express code that tries to serve static files from two directories:

app.use(express.static('public'));
app.use(express.static));
app.use(express.static('assets'));

medium

A. The first line should use app.get instead of app.use.

B. The second line has a syntax error with missing parentheses and argument.

C. Express cannot serve from more than one directory.

D. The third line should come before the first line.

Solution

1. Step 1: Check each line for syntax correctness

   The second line is app.use(express.static)); which is missing parentheses and directory argument.

2. Step 2: Understand correct usage of express.static

   The express.static() function requires a directory path as an argument and proper parentheses.

3. Final Answer:

   The second line has a syntax error with missing parentheses and argument. -> Option B

4. Quick Check:

   Syntax error in express.static call = B [OK]

Hint: Check parentheses and arguments in express.static calls [OK]

Common Mistakes:

• Ignoring missing parentheses or arguments
• Thinking app.use is wrong for static files
• Believing order of calls causes syntax error

5. You want to serve static files from public and uploads directories, but only files in uploads should be accessible under the URL path /files. How do you configure Express correctly?

hard

A. app.use(express.static('public/uploads'));
app.use(express.static('uploads'));

B. app.use('/files', express.static('public'));
app.use(express.static('uploads'));

C. app.use(express.static('public'));
app.use('/files', express.static('uploads'));

D. app.use(express.static('public'));
app.use(express.static('/files/uploads'));

Solution

1. Step 1: Serve public directory normally

   Use app.use(express.static('public')) to serve files at root URL.

2. Step 2: Mount uploads directory under /files path

   Use app.use('/files', express.static('uploads')) so files in uploads are accessible under /files URL prefix.

3. Final Answer:

   app.use(express.static('public')); app.use('/files', express.static('uploads')); -> Option C

4. Quick Check:

   Use URL prefix for uploads folder = A [OK]

Hint: Use URL path prefix in app.use for selective static serving [OK]

Common Mistakes:

• Serving uploads without URL prefix
• Using wrong directory paths
• Confusing URL path with filesystem path