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JavaScript Essentials
1. Variables :-
‣ Declaration: Use `let`, `const`, or `var` to declare variables.
let name = 'Alice'; const age = 30;

2. Data Types :-

‣ Primitive Types: Number, String, Boolean, Null, Undefined, Symbol, BigInt.

‣ Reference Types: Objects, Arrays, Functions.

3. Operators :-

‣ Arithmetic: `+`, `-`, `*`, `/`, `%`.

‣ Assignment: `=`, `+=`, `-=`.

‣ Comparison: `==`, `===`, `!=`, `!==`, `<`, `>`, `<=`, `>=`.

‣ Logical: `&&`, `||`, `!`.

4. Control Structures :-

‣ Conditional Statements: `if`, `else if`, `else`, `switch`.
if (age > 18) { console.log('Adult'); } else { console.log('Minor'); }

‣ Loops: `for`, `while`, `do...while`.
for (let i = 0; i < 5; i++) { console.log(i); }

5. Functions :-

‣ Function Declaration:
function greet(name) { return 'Hello ' + name; }

‣ Arrow Functions:
const greet = (name) => 'Hello ' + name;

6. Objects :-
‣ Creating objects using literal notation:
const person = { name: 'Alice', age: 30, greet() { return 'Hello ' + this.name; } };

7. Arrays :-

‣ Declaring arrays:
const fruits = ['apple', 'banana', 'cherry'];

‣ Array methods: `push()`, `pop()`, `shift()`, `unshift()`, `map()`, `filter()`, `reduce()`.

8. Asynchronous JavaScript :-

‣ Callbacks: Functions passed as arguments.

‣ Promises: For handling asynchronous operations.
let promise = new Promise((resolve, reject) => { // Async operation });

‣ Async/Await: Syntactic sugar for working with promises.
async function fetchData() { let response = await fetch('url'); let data = await response.json(); }

9. DOM Manipulation :-

‣ Selecting elements: `document.querySelector()`, `document.getElementById()`.

‣ Changing content: `element.innerHTML`, `element.style`.

‣ Event handling: `addEventListener()`.
button.addEventListener('click', () => { alert('Button clicked!'); });

10. Error Handling :-
‣ Using `try`, `catch`, and `finally`.
try { // Code that may throw an error } catch (error) { console.error(error); }

11. Modules :-
‣ Importing and exporting functionality between files.
// module.js export const value = 42; // main.js import { value } from './module.js';

JavaScript is versatile for both client-side and server-side programming. Mastering these essentials provides a solid foundation for building dynamic web applications.

JavaScript Essentials

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