Running scripts with node command in Node.js

Introduction

We use the node command to run JavaScript files outside the browser. It lets us see the program's results on our computer.

You want to test a small JavaScript program quickly.

You need to run a server or backend code written in JavaScript.

You want to automate tasks using JavaScript scripts.

You are learning JavaScript and want to try code without a browser.

You want to run JavaScript tools or utilities on your computer.

Syntax

Node.js

node filename.js

Replace filename.js with your JavaScript file name.

Make sure you are in the folder where the file is saved or provide the full path.

Examples

This runs the app.js file in the current folder.

Node.js

node app.js

This runs test.js inside the scripts folder.

Node.js

node ./scripts/test.js

Starts Node.js interactive mode where you can type JavaScript directly.

Node.js

node

Sample Program

This simple program prints a greeting message to the console when run with node.

Node.js

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

Important Notes

If you get an error like 'node: command not found', Node.js might not be installed or added to your system path.

You can stop a running Node.js program by pressing Ctrl + C in the terminal.

Summary

The node command runs JavaScript files on your computer.

Use it to test scripts, run servers, or try JavaScript without a browser.

Make sure your file path is correct and Node.js is installed.

Practice

1. What does the node command do when you run node script.js in your terminal?

easy

A. It uploads script.js to a web server.

B. It opens the script.js file in a text editor.

C. It compiles script.js into a binary executable.

D. It runs the JavaScript code inside the file script.js using Node.js.

Solution

1. Step 1: Understand the purpose of the node command

   The node command runs JavaScript files using the Node.js runtime environment.

2. Step 2: Analyze the command node script.js

   This command tells Node.js to execute the code inside the file named script.js.

3. Final Answer:

   It runs the JavaScript code inside the file script.js using Node.js. -> Option D

4. Quick Check:

   Running node file.js executes the file [OK]

Hint: Node runs JavaScript files given as arguments [OK]

Common Mistakes:

• Thinking node opens files in editors
• Confusing node with a compiler
• Assuming node uploads files

2. Which of the following is the correct way to run a JavaScript file named app.js using Node.js?

easy

A. node run app.js

B. node app.js

C. run node app.js

D. execute app.js with node

Solution

1. Step 1: Recall the correct syntax for running scripts with Node.js

   The correct syntax is node filename.js without extra words.

2. Step 2: Check each option

   node app.js matches the correct syntax exactly: node app.js.

3. Final Answer:

   node app.js -> Option B

4. Quick Check:

   Correct command syntax is node filename.js [OK]

Hint: Use 'node' followed directly by the filename [OK]

Common Mistakes:

• Adding extra words like 'run' or 'execute'
• Swapping order of 'node' and filename
• Using commands not recognized by Node.js

3. Given the file hello.js with this content:

console.log('Hello, Node!');

What will be the output when running node hello.js?

medium

A. Hello, Node!

B. console.log('Hello, Node!');

C. SyntaxError

D. No output

Solution

1. Step 1: Understand what console.log does

   The console.log function prints the text inside the parentheses to the terminal.

2. Step 2: Predict the output of running node hello.js

   Running the file executes the code and prints 'Hello, Node!' to the terminal.

3. Final Answer:

   Hello, Node! -> Option A

4. Quick Check:

   console.log prints text to terminal [OK]

Hint: console.log prints text when run with node [OK]

Common Mistakes:

• Expecting code to print the code itself
• Thinking node throws syntax errors for valid code
• Assuming no output without browser

4. You try to run node myscript.js but get an error: Error: Cannot find module './myscript.js'. What is the most likely cause?

medium

A. The file myscript.js does not exist in the current directory.

B. Your JavaScript code inside myscript.js has a syntax error.

C. You typed node myscript.js incorrectly; it should be node run myscript.js.

D. Node.js is not installed on your computer.

Solution

1. Step 1: Understand the error message

   The error says Node.js cannot find the file myscript.js in the current folder.

2. Step 2: Identify the cause

   This usually means the file is missing or the path is wrong, not that Node.js is missing or the code has syntax errors.

3. Final Answer:

   The file myscript.js does not exist in the current directory. -> Option A

4. Quick Check:

   File missing causes 'Cannot find module' error [OK]

Hint: Check file exists in current folder before running [OK]

Common Mistakes:

• Assuming Node.js is not installed from this error
• Adding extra words to the node command
• Confusing file not found with syntax errors

5. You have two files:

index.js:
console.log('Start');
require('./helper.js');
console.log('End');

helper.js:
console.log('Helper loaded');

What will be the output when you run node index.js?

hard

A. Start
End
Helper loaded

B. Helper loaded
Start
End

C. Start
Helper loaded
End

D. SyntaxError

Solution

1. Step 1: Understand the order of execution in index.js

   The code first prints 'Start', then loads and runs helper.js, then prints 'End'.

2. Step 2: Trace the output step-by-step

   First, 'Start' is printed. Then helper.js runs and prints 'Helper loaded'. Finally, 'End' is printed.

3. Final Answer:

   Start Helper loaded End -> Option C

4. Quick Check:

   require runs the imported file immediately [OK]

Hint: require runs the file immediately in order [OK]

Common Mistakes:

• Assuming require runs after all code
• Mixing output order
• Expecting syntax errors without mistakes