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Lesson 1 of 3

Variables and Data Types

Learn how to store and work with different types of data in JavaScript using variables.

16 minutes

Variables and Data Types

Variables are containers for storing data values in JavaScript.

Declaring Variables

JavaScript has three ways to declare variables:

  • let: Block-scoped, can be reassigned
  • const: Block-scoped, cannot be reassigned
  • var: Function-scoped (older syntax)

Data Types

Primitive Types

  • String: Text data ("Hello World")
  • Number: Numeric values (42, 3.14)
  • Boolean: True or false values
  • Undefined: Variable declared but not assigned
  • Null: Intentional absence of value

Best Practice

Always use const by default, and only use let when you need to reassign the variable.

Code Example

// Using const for values that won't change
const name = "Elena";
const age = 28;
const isStudent = false;

// Using let for values that will change
let score = 0;
score = score + 10;

console.log(`${name} is ${age} years old`);
console.log(`Current score: ${score}`);
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