Express installation and setup - Cheat Sheet & Quick Revision

Recall & Review

beginner

What command do you use to create a new Node.js project before installing Express?

You use npm init -y to quickly create a new Node.js project with default settings.

beginner

How do you install Express in your project?

Run npm install express in your project folder to add Express as a dependency.

beginner

What is the basic code to create an Express app and start a server on port 3000?

```js
const express = require('express');
const app = express();

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(3000, () => {
  console.log('Server running on http://localhost:3000');
});
```

beginner

Why do we use app.listen() in Express?

app.listen() tells Express to start the server and listen for requests on a specific port.

beginner

What file usually contains the Express app setup code?

Typically, the main file is named index.js or app.js where Express is set up and the server starts.

Which command installs Express in your Node.js project?

A express install

B npm start express

C node install express

D npm install express

The correct command is npm install express to add Express to your project.

What does app.listen(3000) do in an Express app?

A Creates a new route

B Stops the server

C Starts the server on port 3000

D Installs Express

app.listen(3000) starts the server and listens for requests on port 3000.

Which file is commonly used to write Express setup code?

A style.css

B index.js

C package.json

D README.md

index.js or app.js usually contain the Express app setup code.

What is the purpose of npm init -y before installing Express?

A Creates a new Node.js project with default settings

B Installs Express globally

C Starts the Express server

D Updates npm to latest version

npm init -y quickly creates a new Node.js project with default settings.

How do you send a simple 'Hello World!' response in Express?

A res.send('Hello World!')

B console.log('Hello World!')

C app.listen('Hello World!')

D npm install 'Hello World!'

Use res.send('Hello World!') inside a route to send a response.

Describe the steps to install Express and start a basic server.

Think about commands and basic code to get Express running.

Explain why we need to use app.listen() in an Express application.

Consider what happens after writing routes.

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