JavaScript Variables

In JavaScript, variables are used to store and manipulate data. They serve as named containers that hold values, which can be of various types, such as numbers, strings, booleans, arrays, objects, and more. Variables in JavaScript are dynamically typed, meaning you don't need to explicitly specify their types.

Here's how you can declare variables in JavaScript:

1. Using the var keyword: The var keyword is used to declare variables. It has function scope or global scope, depending on where it is declared. Variables declared with var are hoisted to the top of their scope, which means they can be accessed before they are declared. However, their values will be undefined until they are assigned a value. Here's an example:

var name = "John"; // Declaring a variable named "name" and assigning it the value "John"

var age; // Declaring a variable named "age" without assigning a value

age = 25; // Assigning the value 25 to the variable "age"

2. Using the let keyword: Introduced in ECMAScript 2015 (ES6), the let keyword allows you to declare block-scoped variables. Block scope means that variables declared with let are only accessible within the block of code where they are defined, such as inside a loop or an if statement. Unlike var, let variables are not hoisted, so they must be declared before they are used. Here's an example:

let name = "John"; // Declaring a block-scoped variable named "name" and assigning it the value "John"

let age; // Declaring a block-scoped variable named "age" without assigning a value

age = 25; // Assigning the value 25 to the variable "age"

3. Using the const keyword: The const keyword is used to declare constants, which are variables that cannot be reassigned after they are initialized. Like let, const also has block scope. Constants must be assigned a value at the time of declaration and cannot be left uninitialized. Here's an example:

const name = "John"; // Declaring a constant named "name" and assigning it the value "John"

const age = 25; // Declaring a constant named "age" and assigning it the value 25

It's important to note that variables declared with var or let can be reassigned with a new value, while constants declared with const cannot be reassigned. However, for objects and arrays declared as constants, their properties or elements can still be modified.

JavaScript variables are flexible and allow you to store and manipulate data throughout your code. By choosing the appropriate variable declaration keyword (var, let, or const), you can control their scope and mutability based on your specific requirements.