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Primitive types

Learn the primitive types string, number, boolean, null, undefined.

Primitive types

In JavaScript, primitive types are the most basic data types: number, string, boolean, null and undefined. They hold a single value and are not objects.

number holds both integers and decimals. string holds text. boolean is only true or false.

null means 'intentionally empty', undefined means 'value not yet assigned'. They are different things.

Five primitive types

Let us briefly meet each of the five primitives:

  • number: 42, 3.14
  • string: 'hello', "world"
  • boolean: true, false
  • null: intentionally empty value
  • undefined: not yet assigned value

We will see these in detail later. For now, knowing all five is enough.

Practice Print three different primitives

Declare three variables: name string 'Alex', count number 7, active boolean true. Call console.log with each.

Starter code

index.js
// Declare name, count and active variables
// Log all three

Sample solution

index.js
const name = "Alex";
const count = 7;
const active = true;
console.log(name);
console.log(count);
console.log(active);

Expected output

Alex
7
true

Questions and answers

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

1 Which one is a primitive type?

  • Array
  • Number Correct answer
  • Object
  • Function

Explanation: number is a primitive type.

2 boolean example

Question 
const isOpen = ____;
Answer 
const isOpen = true;

Explanation: yes or 1 are not booleans.

3 Match the primitive types

Term Meaning
number Number
string Text
boolean Logical
undefined Not defined

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