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.