Data Types

JavaScript is a dynamically typed language, meaning you don't have to specify the data type of a variable when you declare it. The data type is determined automatically based on the value assigned to the variable.

JavaScript has several basic data types that you’ll use frequently:

String

Represents text data. Strings are sequences of characters enclosed in single quotes ('), double quotes ("), or backticks (`).

let greeting = "Hello, world!";
let anotherGreeting = "Hi there!";
let templateString = `Today is ${new Date().toDateString()}`;

Number

Represents numeric data, including integers and floating-point numbers (decimals).

let age = 25;       // Integer
let price = 19.99;  // Floating-point number
let largeNumber = 1e6; // Exponential notation (1 million)

Boolean

Represents a logical value and can be either true or false. Booleans are typically used in conditions and loops to control the flow of your program.

let isLoggedIn = true;
let hasPermission = false;

Undefined

A variable that has been declared but not assigned a value has the type undefined.

let notAssigned;
console.log(notAssigned); // Output: undefined

Null

Represents the intentional absence of any object value. It is often used to indicate that a variable should be empty.

let emptyValue = null;

Undefined vs. Null:

Undefined: When a variable is declared but not assigned a value, it has the value undefined.

Null: Null is an assignment value that represents "no value" or "nothing."

Object

Objects are complex data types that can store collections of data and more complex entities. Arrays, functions, and other objects are also considered objects in JavaScript.

let person = {
  name: "Amir",
  age: 30,
  isEmployed: true
};

Array

Arrays are special types of objects used to store multiple values in a single variable. Each item in an array is called an element, and it is accessed by its index (position) within the array, starting from 0.

let colors = ["Red", "Green", "Blue"];
console.log(colors[0]); // Output: "Red"
console.log(colors[2]); // Output: "Blue"

Some useful methods for Arrays:

Adding elements: You can add elements to an array using the push method (adds to the end) or unshift (adds to the beginning).

colors.push("Yellow"); // Adds "Yellow" to the end
colors.unshift("Purple"); // Adds "Purple" to the beginning

Removing elements: You can remove elements using the pop method (removes from the end) or shift (removes from the beginning).

colors.pop(); // Removes the last element ("Yellow")
colors.shift(); // Removes the first element ("Purple")

Looping through an array: You can loop through the elements of an array using a for loop or the more modern forEach method.

// Using a for loop
for (let i = 0; i < colors.length; i++) {
  console.log(colors[i]);
}

// Using forEach
colors.forEach(color => console.log(color));

Checking the length: The length property returns the number of elements in an array.

console.log(colors.length); // Output: 3

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