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Logical operators

Learn boolean logic with &&, || and !.

Logical operators

Logical operators combine boolean values: && (and), || (or), ! (not).

&& returns true if both conditions are true: age >= 18 && hasLicense. || returns true if at least one is true: isWeekend || isHoliday.

! inverts the value: !isActive. These operators are essential tools for combining conditions.

Short-circuit

Logical operators short-circuit: when the result is determined, they do not evaluate the other side.

For example, in false && something, since the left side is false, the result is definitely false; something is not evaluated. The same goes for true || something.

This is used for safe access: user && user.name. If user is null, the right side does not run; no error is thrown.

Practice Logical expression

Declare age = 20 and hasLicense = true. Compute canDrive as age >= 18 && hasLicense. Call console.log(canDrive).

Starter code

index.js
const age = 20;
const hasLicense = true;
// Compute canDrive as age >= 18 && hasLicense
// Log it with console.log

Sample solution

index.js
const age = 20;
const hasLicense = true;
const canDrive = age >= 18 && hasLicense;
console.log(canDrive);

Expected output

true

Questions and answers

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

1 What does the && operator return?

  • Adds two numbers
  • Compares two values
  • Returns true if both conditions are true Correct answer
  • Returns true if one condition is true

Explanation: && returns true if both conditions are true.

2 Match the operators

Term Meaning
&& Logical and
|| Logical or
! Not
>= Greater or equal

3 && example

Question 
const isValid = age >= 18 ____ hasLicense;
Answer 
const isValid = age >= 18 && hasLicense;

Explanation: && requires both conditions to be true.

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