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What is Node.js?

Learn that Node.js is a V8-based runtime and the event loop.

What is Node.js?

Node.js is a runtime that runs JavaScript outside the browser. It is used to write server applications, command-line tools and scripts.

It is built on Google Chrome's V8 engine and uses the libuv library to perform file and network operations asynchronously. This way it can handle thousands of connections at once efficiently.

Today Node.js 22 LTS is the recommended version. This course uses ES modules syntax.

V8 and the event loop

V8 is Google's open-source JavaScript engine. It is written in C++ and compiles JavaScript into machine code. Node.js uses V8 to execute JavaScript quickly.

The event loop enables Node.js to work asynchronously. When an operation finishes, a callback is triggered. This way the main flow can do other work without blocking.

This model provides high throughput, especially for network and database operations.

Practice Write your first output

Use console.log to print Node.js is running to the screen.

Starter code

index.js
// Write your message here

Sample solution

index.js
console.log("Node.js is running");

Expected output

Node.js is running

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What is Node.js built on?

  • The C# runtime
  • The Python interpreter
  • The Java virtual machine
  • The V8 JavaScript engine Correct answer

Explanation: Node.js is built on the V8 engine.

2 Match the concepts

Term Meaning
Node.js Runtime
V8 JavaScript engine
libuv Event loop library
npm Package manager

3 Run command

Question 
To run a JavaScript file, you type ____ file.js in the terminal.
Answer 
To run a JavaScript file, you type node file.js in the terminal.

Explanation: The node command runs a JavaScript file.

All lessons in Beginner

1 Node.js basics

  1. What is Node.js?
  2. Your first program
  3. ES modules
  4. package.json
  5. CommonJS vs ESM
  6. Summary - Node.js basics

2 Variables

  1. let and const
  2. var and scope
  3. Type inference
  4. Destructuring
  5. Spread and rest
  6. Summary - Variables

3 Data types

  1. Primitive types
  2. Template literals
  3. Number and Math
  4. Symbol
  5. typeof
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. process.argv
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Nullish coalescing
  6. Summary - Operators

6 Strings

  1. String methods
  2. String search
  3. substring and slice
  4. replace and split
  5. padStart and trim
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. switch
  4. Ternary
  5. Optional chaining
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. for...of
  4. for...in
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. push and pop
  4. shift and unshift
  5. splice and slice
  6. Summary - Arrays

11 Array methods

  1. map
  2. filter
  3. reduce
  4. find and some
  5. forEach
  6. Summary - Array methods

12 Objects

  1. Object literal
  2. Property access
  3. Computed properties
  4. Object methods
  5. Object spread
  6. Summary - Objects

13 Functions

  1. Defining functions
  2. Return values
  3. Arrow functions
  4. Default parameters
  5. Rest parameters
  6. Summary - Functions

14 Callbacks

  1. What are callbacks?
  2. Higher-order functions
  3. forEach with callbacks
  4. Error-first callbacks
  5. Callback hell
  6. Summary - Callbacks

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Promises

  1. What are promises?
  2. then and catch
  3. Promise.all
  4. Promise.race
  5. finally
  6. Summary - Promises

17 async/await

  1. async function
  2. await
  3. try/catch
  4. await with Promise.all
  5. Sequential await
  6. Summary - async/await

18 fs module

  1. fs.promises
  2. readFile
  3. writeFile
  4. appendFile
  5. existsSync
  6. Summary - fs module

19 path module

  1. path.join
  2. path.resolve
  3. path.parse
  4. path.dirname and basename
  5. path.extname
  6. Summary - path module

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. fs persistence
  5. Putting it together