JavaScript Basics

In this section, we will explore the basics of JavaScript, a versatile and widely-used programming language that plays a pivotal role in web development. JavaScript is primarily known for its client-side scripting capabilities, empowering developers to create interactive and dynamic web applications that enhance user experience.

Variables and Data Types:

In JavaScript, variables and data types are fundamental concepts that form the backbone of the language. Understanding how to declare variables and work with different data types is crucial for writing high-quality and efficient JavaScript code. 

A variable is a named container used to store data values in JavaScript. The data stored in a variable can be of different types, such as numbers, strings, booleans, arrays, objects, and more. 

Before using a variable needs to be declared using the var, let, or const keywords before it is used. The choice of the keyword can affect the variable's scope and mutability.

a. var: Historically used to declare variables, but it has some issues related to scoping. Variables declared with var are function-scoped or globally-scoped, leading to unintended side effects and making code harder to maintain.

b. let: Introduced in ECMAScript 6 (ES6), let allows block-scoped variables. Variables declared with let are limited to the block in which they are defined, such as within loops or conditionals. This helps prevent variable pollution and unintended modifications.

c. const: Also introduced in ES6, const declares constant variables with block scope. The value of a constant cannot be reassigned after its initial assignment, making it useful for creating read-only variables.

Data Types in JavaScript:

JavaScript is a dynamically-typed language, meaning variables can hold different data types, and their types can change during runtime. The following are the primary data types in JavaScript:

Numbers

Numeric data type representing both integers and floating-point numbers.

let age = 30; // Integer
let pi = 3.14; // Floating-point number

Strings

Sequences of characters, enclosed in single ('') or double ("") quotes.

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

Booleans

Represents true or false values, useful for conditional expressions.

let isStudent = true;
let isWorking = false;

Arrays

Ordered collections of elements, denoted by square brackets ([]).

let fruits = ['apple', 'banana', 'orange'];

Objects

Unordered collections of key-value pairs, denoted by curly braces ({})

let person = {
 name: 'John Doe',
 age: 25,
 isStudent: true,
};

Undefined and Null

undefined represents a variable declared but not assigned a value, while null represents an explicitly empty value.

let someVar; // undefined
let emptyValue = null;

Symbols

ES6 introduces symbols as unique and immutable data types primarily used as object property keys.

const idSymbol = Symbol('id');
 let person = {
 [idSymbol]: 123,
};

Functions

Functions are first-class citizens in JavaScript, meaning they can be assigned to variables, passed as arguments, and returned from other functions.

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