1. JavaScript Basics

JavaScript is a lightweight, interpreted programming language that is designed for creating network-centric applications.

1. Print and Alert

console.log("Hello Devendra Dora");
alert("Hello Devendra Dora");

2. Variables

• Variables declared with var are function-scoped or globally scoped.
• Variables declared with let are block-scoped.
• Constants declared with const cannot be reassigned.

var firstName = "Devendra"; // function-scoped or globally scoped
let lastName = "Dor"; // are block-scoped
firstName ="Devendra Kumar"
lastName = "Dora"
console.log("Hello "+firstName+" "+lastName) // concatenate strings with +

const PI = 3.14; // cannot be reassigned
// Attempting to reassign a const variable will result in an error
// PI = 3.14159; // TypeError: Assignment to constant variable.     
console.log(PI);

4. Data Types

JavaScript has data types: Number, String, Boolean, Undefined, Null, Object

• Primitive Data Types:

  • Number: Represents numeric values. It can be integer or floating-point.

  let num = 10;
  let floatNum = 3.14;
  
  

  • bigint
  • String: Represents a sequence of characters, enclosed in single or double quotes.

  let name = "Devendra Dora";
  let message = 'Hello MentorX';
  
  

  • Boolean: Represents a logical value, either true or false.

  let isStudent = true;
  let hasLicense = false;
  
  

  • Undefined: Represents an uninitialised variable or a function that doesn't return a value.

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

  • Null: Represents an intentional absence of any value.

  let y = null;
  console.log(y);
  

  • Symbol (ES6+): Represents a unique identifier, introduced in ES6.

  const sym1 = Symbol();
  const sym2 = Symbol('description');