Variables and Datatypes in JavaScript

Variables and Data Types in JavaScript are fundamental concepts used to store and manage data in a program. They define how information is declared, stored, and manipulated during execution.

Variables: Declared using var, let, and const to store data values.
Primitive Data Types: Includes Number, String, Boolean, Null, Undefined, BigInt, and Symbol.
Non-Primitive Data Types: Includes Object, Array, and Function used to store complex data.

Variables

A variable is like a container that holds data that can be reused or updated later in the program. In JavaScript, variables are declared using the keywords var, let, or const.

var Keyword The var keyword is used to declare a variable. It has a function-scoped or globally-scoped behaviour.

var n = 5;
console.log(n);

var n = 20; // reassigning is allowed
console.log(n);

let Keyword The let keyword is introduced in ES6, has block scope and cannot be re-declared in the same scope.

let  n= 10;
n = 20; // Value can be updated
// let n = 15; //can not redeclare
console.log(n)

const Keyword The const keyword declares variables that cannot be reassigned. It's block-scoped as well.

const n = 100;
// n = 200; This will throw an error
console.log(n)

4.without keyword
In this we can reinsilate and it prints the last value declare.

i=10;
i=20;
console.log(i)

Data Types

JavaScript supports various datatypes, which can be broadly categorized into primitive and non-primitive types.

Primitive Datatypes
Primitive datatypes represent single values and are immutable.

Number: Represents numeric values (integers and decimals).

let n = 42;
let pi = 3.14;

String: Represents text enclosed in single or double quotes.

let s = "Hello, World!";

Boolean: Represents a logical value (true or false).

let bool= true;

Undefined: A variable that has been declared but not assigned a value.

let notAssigned;
console.log(notAssigned);

Null: Represents an intentional absence of any value.

let empty = null;

Symbol: Represents unique and immutable values, often used as object keys.

let sym = Symbol('unique');

BigInt: Represents integers larger than Number.MAX_SAFE_INTEGER.We can denote BigInt by using n at the end or the values.

let bigNumber = 123456789012345678901234567890n;

Non-Primitive Datatypes
Non-primitive types are objects and can store collections of data or more complex entities.

Object: Represents key-value pairs.

let obj = {
    name: "Amit",
    age: 25
};

Array: Represents an ordered list of values.

let a = ["red", "green", "blue"];

Function: Represents reusable blocks of code.

function fun() {
    console.log("GeeksforGeeks");
}

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Variables and Datatypes in JavaScript