Express installation and setup - Practice Problems & Coding Challenges

Challenge - 5 Problems

📝 Syntax

intermediate

Identify the correct command to install Express locally

Which command correctly installs Express as a local dependency in your Node.js project?

A npm install express

B npm install -g express

C npm add express

D node install express

💡 Hint

Think about installing packages for your project, not globally.

The command npm install express installs Express locally in your project folder, which is the standard way to add dependencies.

npm install -g express installs Express globally, which is not typical for libraries used in projects.

node install express is not a valid command.

npm add express is not a valid npm command.

❓ component_behavior

intermediate

What happens when you run this Express setup code?

Given the following Express app code, what will be the output when you visit http://localhost:3000/ in a browser?

Express

import express from 'express';
const app = express();
app.get('/', (req, res) => {
  res.send('Hello World!');
});
app.listen(3000);

A The browser shows the text 'Hello World!'

B The browser shows a 404 Not Found error

C The server crashes with an error

D The browser shows a blank page

💡 Hint

Check the route and response sent by the server.

The app listens on port 3000 and responds to GET requests at '/' with 'Hello World!'. Visiting http://localhost:3000/ will display that text.

🔧 Debug

advanced

Why does this Express app fail to start?

Consider this Express app code snippet. Why does running it cause an error?

Express

const express = require('express')
const app = express()
app.get('/', (req, res) => {
  res.send('Hi')
})
app.listen(3000

A No error, app runs fine

B ReferenceError because express is not imported correctly

C TypeError because res.send is not a function

D SyntaxError due to missing closing parenthesis in app.listen

💡 Hint

Check the parentheses in the last line carefully.

The app.listen(3000 line is missing a closing parenthesis, causing a SyntaxError.

The other options are incorrect because express is imported correctly with require, and res.send is valid.

🧠 Conceptual

advanced

What is the purpose of the 'express()' function call?

In Express, what does calling express() do?

A Starts the server listening on a port

B Creates an Express application instance to handle requests and responses

C Imports the Express library into the project

D Defines a route handler for incoming requests

💡 Hint

Think about what you need before defining routes or starting the server.

The express() function creates an app object that you use to define routes and middleware, and to start the server.

Starting the server is done with app.listen().

❓ state_output

expert

What is the value of 'port' after running this code?

Given this Express setup code, what is the value of the variable port after execution?

Express

import express from 'express';
const app = express();
const port = process.env.PORT || 3000;
app.listen(port);

A Undefined because process.env.PORT is not set

B Always 3000 regardless of environment variables

C 3000 if no PORT environment variable is set, otherwise the value of PORT

D Throws an error because process.env is not defined

💡 Hint

Check how the logical OR operator works in JavaScript.

The expression process.env.PORT || 3000 means if process.env.PORT is set (truthy), use it; otherwise, use 3000.

This allows the app to use a port from environment variables or default to 3000.

Practice

1. What command do you use to install Express in a Node.js project?

easy

A. npm install express

B. node install express

C. express install

D. npm start express

Solution

1. Step 1: Understand Node.js package installation

   Node.js packages are installed using the npm tool with the command npm install <package-name>.

2. Step 2: Identify the correct package name for Express

   The package name for Express is exactly "express", so the command is npm install express.

3. Final Answer:

   npm install express -> Option A

4. Quick Check:

   Express installation command = npm install express [OK]

Hint: Use npm install followed by package name [OK]

Common Mistakes:

• Using 'node install' instead of 'npm install'
• Typing 'express install' which is invalid
• Trying to start express with npm start express

2. Which of the following is the correct way to import Express and create an app instance?

easy

A. const express = require('express'); const app = express();

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

C. const app = require('express'); app = express();

D. const express = import('express'); const app = express();

Solution

1. Step 1: Recognize CommonJS import syntax

   In many Node.js projects, Express is imported using CommonJS syntax: const express = require('express');.

2. Step 2: Create app instance correctly

   After importing, the app instance is created by calling express(), so const app = express(); is correct.

3. Final Answer:

   const express = require('express'); const app = express(); -> Option A

4. Quick Check:

   Import Express and create app = require + express() [OK]

Hint: Use require('express') then call express() [OK]

Common Mistakes:

• Using import without proper module setup
• Calling require('express')() directly without variable
• Using import as a function

3. What will the following code do when run?

const express = require('express');
const app = express();
app.get('/', (req, res) => res.send('Hello World'));
app.listen(3000, () => console.log('Server started'));

medium

A. Start a server but does not respond to any requests

B. Throw an error because app.listen is missing a callback

C. Respond with 'Hello World' without starting a server

D. Start a server on port 3000 that responds with 'Hello World' at root URL

Solution

1. Step 1: Analyze server setup and route

   The code creates an Express app, sets a GET route for '/' that sends 'Hello World'.

2. Step 2: Understand app.listen behavior

   The server listens on port 3000 and logs 'Server started' when ready, so it starts correctly.

3. Final Answer:

   Start a server on port 3000 that responds with 'Hello World' at root URL -> Option D

4. Quick Check:

   Express server with route '/' = Hello World response [OK]

Hint: app.listen starts server; app.get defines response [OK]

Common Mistakes:

• Thinking app.listen needs a callback to work
• Assuming no response because of missing middleware
• Confusing route setup with server start

4. Identify the error in this Express setup code:

const express = require('express');
const app = express;
app.listen(3000);

medium

A. app.listen needs a callback function

B. Missing parentheses when creating app instance

C. express should be imported with import, not require

D. app.listen requires a port number as a string

Solution

1. Step 1: Check app instance creation

   The code assigns app = express without calling it. It should be express() to create the app instance.

2. Step 2: Verify app.listen usage

   Calling app.listen(3000) is correct; port number is a number, and callback is optional.

3. Final Answer:

   Missing parentheses when creating app instance -> Option B

4. Quick Check:

   express() must be called to create app [OK]

Hint: Remember to call express() with parentheses [OK]

Common Mistakes:

• Assigning app = express instead of app = express()
• Passing port as string instead of number (allowed but not required)
• Thinking callback in listen is mandatory

5. You want to create an Express server that listens on port 8080 and responds with 'Welcome!' at the root URL. Which code snippet correctly does this?

hard

A. const express = require('express'); const app = express(); app.listen(8080, () => console.log('Server running'));

B. const express = require('express'); const app = express; app.get('/', (req, res) => res.send('Welcome!')); app.listen(8080);

C. const express = require('express'); const app = express(); app.get('/', (req, res) => res.send('Welcome!')); app.listen(8080);

D. const express = require('express'); const app = express(); app.get('/', (req, res) => res.send('Welcome!')); app.listen('3000');

Solution

1. Step 1: Create app instance correctly

   Use const app = express(); to create the Express app instance.

2. Step 2: Define route and start server on port 8080

   Set up app.get('/', ...) to respond with 'Welcome!' and call app.listen(8080); to start the server.

3. Final Answer:

   const express = require('express'); const app = express(); app.get('/', (req, res) => res.send('Welcome!')); app.listen(8080); -> Option C

4. Quick Check:

   Express app with route and listen on 8080 = const express = require('express'); const app = express(); app.get('/', (req, res) => res.send('Welcome!')); app.listen(8080); [OK]

Hint: Call express(), define route, then listen on port [OK]

Common Mistakes:

• Not calling express() to create app
• Passing port as string instead of number (allowed but inconsistent)
• Starting server without defining route