Running JavaScript using Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Node.js?

Node.js is a program that lets you run JavaScript code outside a web browser, usually on your computer or server.

beginner

How do you run a JavaScript file named app.js using Node.js?

Open your terminal or command prompt and type node app.js, then press Enter.

beginner

What does the command node do when used alone in the terminal?

It opens an interactive JavaScript shell where you can type and run JavaScript commands one by one.

beginner

Why might you want to use Node.js instead of running JavaScript in a browser?

Node.js lets you run JavaScript on your computer or server to build apps, work with files, or create servers, which browsers can't do alone.

beginner

What is the first step to run JavaScript with Node.js after installing it?

Open your terminal or command prompt, navigate to the folder with your JavaScript file, then run node filename.js.

Which command runs a JavaScript file named script.js using Node.js?

A js run script.js

B node script.js

C run script.js

D execute script.js

The correct command to run a JavaScript file with Node.js is node filename.js.

What does Node.js allow you to do?

A Create CSS styles

B Only run JavaScript inside browsers

C Write HTML code

D Run JavaScript outside the browser

Node.js lets you run JavaScript code outside the browser, on your computer or server.

What happens if you type node alone in the terminal?

A Starts an interactive JavaScript shell

B Runs the last JavaScript file

C Shows Node.js version

D Opens a text editor

Typing node alone opens a REPL (Read-Eval-Print Loop) where you can type JavaScript commands interactively.

Before running a JavaScript file with Node.js, what should you do?

A Open terminal and go to the file's folder

B Open the file in a browser

C Restart your computer

D Install a web server

You need to open your terminal and navigate to the folder where your JavaScript file is saved before running it.

Which of these is NOT a use case for Node.js?

A Running JavaScript on a server

B Building web servers

C Styling web pages with CSS

D Working with files on your computer

Node.js does not style web pages; CSS is used for styling in browsers.

Explain how to run a JavaScript file using Node.js from start to finish.

Think about what you do in the terminal step by step.

Describe what Node.js is and why it is useful.

Imagine explaining Node.js to a friend who only knows JavaScript runs in browsers.

Practice

1. What does the command node filename.js do?

easy

A. Runs the JavaScript code inside filename.js using Node.js

B. Opens the file filename.js in a text editor

C. Compiles filename.js into a different programming language

D. Deletes the file filename.js from your computer

Solution

1. Step 1: Understand the command node filename.js

   This command tells Node.js to run the JavaScript code inside the file named filename.js.

2. Step 2: Identify what Node.js does

   Node.js executes JavaScript code outside the browser, so it runs the code in the file.

3. Final Answer:

   Runs the JavaScript code inside filename.js using Node.js -> Option A

4. Quick Check:

   node filename.js runs code = C [OK]

Hint: Node runs JavaScript files given after the command [OK]

Common Mistakes:

• Thinking it opens the file in an editor
• Confusing running with compiling
• Assuming it deletes the file

2. Which of the following is the correct way to start an interactive Node.js session in the terminal?

easy

A. run node

B. node filename.js

C. node

D. start node.js

Solution

1. Step 1: Recall how to start Node.js interactively

   Typing node alone in the terminal starts an interactive JavaScript session.

2. Step 2: Check other options

   node filename.js runs a file, not interactive mode; run node and start node.js are invalid commands.

3. Final Answer:

   node -> Option C

4. Quick Check:

   Just node starts interactive mode [OK]

Hint: Just type 'node' to enter interactive mode [OK]

Common Mistakes:

• Adding extra words like 'run' or 'start'
• Confusing running a file with interactive mode
• Using file names when none are needed

3. What will be the output when running this file with node test.js?

console.log('Hello from Node.js!');

medium

A. SyntaxError

B. Hello from Node.js!

C. undefined

D. No output

Solution

1. Step 1: Understand the code inside test.js

   The code uses console.log to print a string to the console.

2. Step 2: Know what Node.js does when running the file

   Node.js executes the code and prints the string to the terminal.

3. Final Answer:

   Hello from Node.js! -> Option B

4. Quick Check:

   console.log prints text = Hello from Node.js! [OK]

Hint: console.log prints output to terminal [OK]

Common Mistakes:

• Expecting no output
• Confusing console.log with return value
• Thinking it causes an error

4. You try to run node app.js but get an error: SyntaxError: Unexpected token. What is the most likely cause?

medium

A. You typed node incorrectly

B. You forgot to save app.js before running

C. Node.js is not installed on your computer

D. The app.js file has invalid JavaScript syntax

Solution

1. Step 1: Understand the error message

   A SyntaxError: Unexpected token means the JavaScript code has a syntax mistake.

2. Step 2: Check other options

   Typing node wrong usually gives a different error; missing Node.js causes 'command not found'; unsaved file won't run but usually no syntax error.

3. Final Answer:

   The app.js file has invalid JavaScript syntax -> Option D

4. Quick Check:

   SyntaxError means code syntax is wrong [OK]

Hint: SyntaxError means code inside file is wrong [OK]

Common Mistakes:

• Assuming Node.js is missing
• Thinking the command was typed wrong
• Not saving file before running

5. You want to quickly test a small JavaScript expression without creating a file. What is the best way to do this using Node.js?

hard

A. Run node in terminal to open interactive mode and type the expression

B. Create a file, write the code, then run node filename.js

C. Use npm start to run the expression

D. Open a browser and run the code in the console

Solution

1. Step 1: Identify how to run code without a file

   Running node alone opens an interactive session where you can type JavaScript directly.

2. Step 2: Compare other options

   Creating a file is slower; npm start runs scripts defined in package.json, not quick tests; browser console is outside Node.js environment.

3. Final Answer:

   Run node in terminal to open interactive mode and type the expression -> Option A

4. Quick Check:

   Interactive mode = quick testing [OK]

Hint: Use just 'node' to test code quickly without files [OK]

Common Mistakes:

• Thinking npm start runs any code
• Believing browser console is Node.js
• Always creating files for small tests