Variables and Data Types

Learn how to store and manipulate data in JavaScript!

Learning Objectives

Understand what variables are
Learn about different data types
Practice declaring and using variables

Explanation

Variables are like containers that store data. In JavaScript, you can create variables using let, const, or var: - let: Declares a variable that can be reassigned (modern approach). - const: Declares a constant variable that cannot be reassigned (modern approach). - var: Older way to declare variables (try to use let and const instead). JavaScript has several data types: 1. Primitive Types: - String: Text (e.g., "Hello") - Number: Numbers (e.g., 42, 3.14) - Boolean: true or false - undefined: Variable declared but not assigned a value - null: Intentional absence of any value - Symbol: Unique and immutable values (advanced) 2. Object Types: - Object: Collections of related data - Array: Ordered lists - Function: Reusable blocks of code JavaScript is "dynamically typed," which means variables can change types. But it's generally good practice to keep a variable's type consistent.

Code Example

// Variable declarations
let name = "Luke Skywalker";  // String
let age = 19;                 // Number
let isJedi = true;            // Boolean

// Constants (can't be reassigned)
const GRAVITY = 9.8;

// Multiple declarations
let planet = "Tatooine", 
    system = "Outer Rim",
    hasWater = false;

// Changing variable values
name = "Luke"; // This works with let
// GRAVITY = 10; // This would cause an error with const

// Different types of data
let jediKnight = {    // Object
  name: "Obi-Wan",
  age: 38,
  lightsaberColor: "blue"
};

let droids = ["R2-D2", "C-3PO", "BB-8"];  // Array

// Checking types
console.log(typeof name);      // "string"
console.log(typeof age);       // "number"
console.log(typeof isJedi);    // "boolean"
console.log(typeof jediKnight); // "object"
console.log(typeof droids);     // "object" (arrays are objects in JS)

Try It Yourself!

Try creating variables to store information about yourself, like name, age, and favorite color!

JavaScript Editor

Mini Quiz

Test your knowledge with these quick questions!

1. Which keyword is used to declare a variable that cannot be reassigned?

let

var

const

fixed

2. What will typeof [1, 2, 3] return?

'array'

'number'

'object'

'list'

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Est. time: 15-20 min

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