JavaScript

JavaScript (JS) is a high-level, interpreted programming language originally designed for adding interactivity to web pages. Today, it is a multi-paradigm language used across web development, backend services, mobile apps, and even desktop applications.

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1. Brief History of JavaScript

• 1995 – Brendan Eich at Netscape created JavaScript in just 10 days, originally named Mocha, later renamed LiveScript, and finally JavaScript (partly for marketing, to ride on Java’s popularity).
• 1996 – Microsoft introduced JScript (their implementation for IE 3).
• 1997 – Standardized as ECMAScript (ES) by ECMA International (ECMA-262 spec).
• 2009 – Node.js brought JS to the server.
• 2015 onwards – ES6 (aka ES2015) revolutionized JS with modern features.

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2. Major ECMAScript (ES) Version Updates

Year	Version	Key Features
1997	ES1	First edition
1998	ES2	Minor changes
1999	ES3	Regular expressions, better error handling
2009	ES5	Strict mode, JSON support, Array.forEach, getters/setters
2015	ES6 (ES2015)	let, const, classes, modules, template literals, arrow functions, promises, default/rest/spread params
2016	ES7	Array.includes, exponentiation (**)
2017	ES8	async/await, Object.entries, Object.values
2018	ES9	Rest/spread in objects, async iterators
2019	ES10	Array.flat, Object.fromEntries, optional catch binding
2020	ES11	Optional chaining (?.), nullish coalescing (??), dynamic import()
2021+	ES12+	Logical assignment (`		=, ??=), String.replaceAll, top-level await`, weak references, etc.

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3. JavaScript Features with Examples

A. Basic Features

1. Variables

var x = 5;   // function-scoped
let y = 10;  // block-scoped
const z = 15; // immutable

2. Data Types

let num = 42;        // number
let str = "Hello";   // string
let bool = true;     // boolean
let obj = {a:1};     // object
let arr = [1,2,3];   // array
let n = null;        // null
let u;               // undefined

3. Functions

function add(a, b) {
  return a + b;
}
console.log(add(2,3));

4. Control Flow

for (let i=0; i<3; i++) console.log(i);

if (true) console.log("Yes");

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B. Intermediate Features

1. Arrow Functions

const multiply = (a, b) => a * b;

2. Template Literals

let name = "Alice";
console.log(`Hello, ${name}!`);

3. Destructuring

const [a,b] = [1,2];
const {x, y} = {x:10, y:20};

4. Spread / Rest

let nums = [1,2,3];
let more = [...nums, 4,5];

function sum(...args) {
  return args.reduce((a,b)=>a+b, 0);
}

5. Classes

class Person {
  constructor(name) { this.name = name; }
  greet() { console.log(`Hi, I'm ${this.name}`); }
}

6. Modules (ES6)

// file: math.js
export const add = (a,b) => a+b;

// file: app.js
import { add } from './math.js';

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C. Advanced Features

1. Promises & Async/Await

function fetchData() {
  return new Promise(resolve => setTimeout(()=>resolve("Done"), 1000));
}

async function run() {
  let result = await fetchData();
  console.log(result);
}
run();

2. Generators

function* numbers() {
  yield 1;
  yield 2;
  yield 3;
}
for (let n of numbers()) console.log(n);

3. Optional Chaining

let user = {profile: {name: "Alice"}};
console.log(user.profile?.name); // Alice
console.log(user.settings?.theme); // undefined

4. Nullish Coalescing

let x = null ?? "default"; // "default"

5. Proxies

let obj = {a:1};
let proxy = new Proxy(obj, {
  get: (target, prop) => prop in target ? target[prop] : "Not found"
});
console.log(proxy.a, proxy.b);

6. Symbols & Iterators

const sym = Symbol("id");
let obj2 = {[sym]: 123};
console.log(obj2[sym]);

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4. Flavours of JavaScript Implementations

JavaScript isn’t just one runtime—it has multiple implementations:

Implementation	Environment	Highlights
Browser JS	Runs inside browsers (V8 in Chrome, SpiderMonkey in Firefox, JavaScriptCore in Safari)	DOM manipulation, events, APIs
Node.js	Server-side runtime (uses V8)	File system, networking, backend services
Deno	Secure JS/TS runtime by Node’s creator	Built-in TypeScript, secure by default, ES modules
Bun	New runtime (powered by Zig & JavaScriptCore)	Very fast, built-in bundler, test runner
Nashorn/GraalJS	Java-based implementations	Running JS on JVM
Adobe’s ExtendScript	Adobe apps scripting	Automates Photoshop/Illustrator

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Summary:

• JS started in 1995, standardized as ECMAScript.
• ES6 (2015) was the biggest leap with modern syntax.
• Features range from basics (variables, functions) → intermediate (classes, modules) → advanced (async/await, proxies, generators).
• Multiple runtimes exist: browsers, Node.js, Deno, Bun, etc.