Data Types and Variables

In JavaScript, data types and variables are fundamental concepts that you’ll frequently encounter when coding. Here’s a breakdown of the basic data types, variables, and how they are used, with examples:

Data Types

JavaScript has several basic data types:

1. Primitive Data Types:

• Number: Represents both integer and floating-point numbers.

let age = 25; // Integer
let temperature = 98.6; // Floating-point number

• String: Represents a sequence of characters.

let name = "John Doe";
let greeting = 'Hello, World!';

• Boolean: Represents a value of either true or false

let isActive = true;
let isCompleted = false;

• Undefined: Represents a variable that has been declared but not yet assigned a value.

let user; // undefined

• Null: Represents the intentional absence of any object value

let emptyValue = null;

• Symbol: Represents a unique and immutable value used as an object property key.

const uniqueID = Symbol('id');

• BigInt: Represents integers with arbitrary precision

let largeNumber = 1234567890123456789012345678901234567890n;

2. Object Data Types:

• Object: Represents a collection of properties, where each property is a key-value pair.

let person = {
  firstName: "Jane",
  lastName: "Doe",
  age: 30
};

• Array: A special type of object used for storing ordered collections of values

let numbers = [1, 2, 3, 4, 5];
let colors = ["red", "green", "blue"];

• Function: A type of object that represents executable code

function greet(name) {
  return `Hello, ${name}!`;
}

Variables

Variables in JavaScript are used to store data that can be referenced and manipulated. You can declare variables using var, let, or const:

1. var:

• Oldest way to declare variables, function-scoped.

var x = 10;

• Can lead to issues due to hoisting and scoping quirks.

2. let:

• Block-scoped, introduced in ES6 (ECMAScript 2015).

let y = 20;

• Useful for variables that change.

3. const:

• Block-scoped, but the variable’s value cannot be reassigned after initialization.

const z = 30;

• Best for constants and values that shouldn’t change.

Examples

1. Basic Variable Usage:

let name = "Alice";
let age = 28;
const pi = 3.14159;

console.log(name); // Output: Alice
console.log(age);  // Output: 28
console.log(pi);   // Output: 3.14159

2. Using Different Data Types:

let isRaining = true; // Boolean
let temperature = 72.5; // Number (float)
let city = "San Francisco"; // String
let data = [1, 2, 3, 4]; // Array
let person = { name: "Bob", age: 40 }; // Object

console.log(isRaining); // Output: true
console.log(temperature); // Output: 72.5
console.log(city); // Output: San Francisco
console.log(data); // Output: [1, 2, 3, 4]
console.log(person.name); // Output: Bob

3. Function Example:

function add(a, b) {
  return a + b;
}

let sum = add(5, 10);
console.log(sum); // Output: 15

Summary

• Primitive data types are basic and immutable.
• Object data types include objects, arrays, and functions, and are mutable.
• Variables store data and can be declared using var, let, or const.

Understanding these data types and variable declarations is fundamental to start writing JavaScript programs.