Day 1 of JavaScript

What is JavaScript?

JavaScript (JS) is a scripting language used to make web pages interactive. It runs in the browser and allows developers to create dynamic content like pop-ups, animations, and form validation.

Variables in JavaScript

JavaScript Variables can be declared in 4 ways:

var
let
const

Var

var is used to declare variables, we can also redeclare and update using var

var name = "Geetha"; 
var name = "Haveela"; 
console.log(name); //Output: Haveela

Let

let is used to declare variables, we can update variables using let but we can’t redeclare them.

let i=22;
i=30; 
console.log(i); //Output: 30

Const

Const is used to declare variables, here we can not update or redeclare varibles.

const name="Geetha";
name="Haveela"; //we will get an error message

Data Types in JavaScript

JavaScript has two main types of data:

Primitive Data Types

Data Type	Example
Number	`let a=5;`
String	`let name="Geetha";`
Boolean	`let isStudent=true;`
Null	`let value=null;`
Undefined	`let a;`
Symbol	`let id=Symbol("id");`
BigInt	`let big= 99999999999999999;`

Reference Data Types

Data Type	Example
Object	`let names={name:"Geetha",age:22};`
Array	`let names=["Geetha","Haveela","Rishitha"];`
Typeof	`typeof "name" //Returns "string"`

Operators in JavaScript

Arithmetic Operators (Math operations)

Operator	Description	Example
+	Addition	5+2 // 7
-	Subtraction	5-2 // 3
*	Multiplication	5×2 //10
/	Division	10/2 //5
%	Modulus (Remainder)	10%3 // 1
**	Exponentiation	2**3 // 8

Comparison Operators (Returns true or false)

Operator	Description	Example
\==	qual to	`5 == "5" // true`
\===	Strict equal (checks type & value)	`5 === "5" // false`
≠	Not equal	`5 != 3 // true`
≠=	Strict not equal	`5 !== "5" // true`
\>;	Greater than	`10 > 5 // true`
<	Less than	`10 < 5 // false`

Logical Operators

Operator	Description	Example
`&&`	AND	`(5 > 3 && 10 > 5) // true`
`!`	NOT	`!(5 > 3) // false`

Control Flow

if-else

let age = 18;

if (age >= 18) {
  console.log("You are an adult");
} else {
  console.log("You are a minor");
}

switch

let day = "Monday";
switch (day) {
  case "Monday":
    console.log("Start of the week!");
    break;
  case "Friday":
    console.log("Weekend is near!");
    break;
  default:
    console.log("Just another day!");
}