⚡ JavaScript Programming Language

// Variable declarations var oldStyle = "function-scoped"; let blockScoped = "block-scoped"; const constant = "cannot be reassigned"; // Multiple declarations let x = 1, y = 2, z = 3; // Destructuring assignment const [a, b, c] = [1, 2, 3]; const {name, age} = {name: "John", age: 30}; // Template literals const message = `Hello, ${name}! You are ${age} years old.`;

// Primitive types let string = "Hello World"; let number = 42; let bigint = 123n; let boolean = true; let undefined_var; let null_var = null; let symbol = Symbol("id"); // Objects let object = {key: "value"}; let array = [1, 2, 3]; let func = function() {}; // Type checking typeof variable; Array.isArray(variable); variable instanceof Constructor;

// Arithmetic + - * / % ** // Assignment = += -= *= /= %= **= // Comparison == === != !== < > <= >= // Logical && || ! // Bitwise & | ^ ~ << >> >>> // Ternary condition ? valueIfTrue : valueIfFalse // Nullish coalescing value ?? defaultValue // Optional chaining object?.property?.method?.()

// If statement if (condition) { // code } else if (anotherCondition) { // code } else { // code } // Switch statement switch (value) { case 'option1': // code break; case 'option2': case 'option3': // code for option2 or option3 break; default: // default code }

// For loop for (let i = 0; i < 10; i++) { console.log(i); } // For...in loop (object properties) for (let key in object) { console.log(key, object[key]); } // For...of loop (iterable values) for (let value of array) { console.log(value); } // While loop while (condition) { // code } // Do-while loop do { // code } while (condition); // Break and continue break; // exit loop continue; // skip to next iteration

// Function declaration function greet(name) { return `Hello, ${name}!`; } // Function expression const greet = function(name) { return `Hello, ${name}!`; }; // Arrow functions const greet = (name) => `Hello, ${name}!`; const add = (a, b) => a + b; const multiply = (a, b) => { return a * b; }; // Default parameters function greet(name = "World") { return `Hello, ${name}!`; } // Rest parameters function sum(...numbers) { return numbers.reduce((a, b) => a + b, 0); } // Destructuring parameters function greet({name, age}) { return `Hello, ${name}! You are ${age} years old.`; }

// Function that returns a function function createMultiplier(factor) { return function(number) { return number * factor; }; } // Function that takes a function as parameter function applyOperation(arr, operation) { return arr.map(operation); } // Immediately Invoked Function Expression (IIFE) (function() { console.log("IIFE executed"); })(); // Callback functions setTimeout(() => { console.log("Delayed execution"); }, 1000);

// Class declaration class Person { // Constructor constructor(name, age) { this.name = name; this.age = age; } // Instance method greet() { return `Hello, I'm ${this.name}`; } // Static method static species() { return "Homo sapiens"; } // Getter get info() { return `${this.name} is ${this.age} years old`; } // Setter set age(value) { if (value > 0) { this._age = value; } } } // Inheritance class Student extends Person { constructor(name, age, studentId) { super(name, age); this.studentId = studentId; } study() { return `${this.name} is studying`; } }

// Constructor function function Person(name, age) { this.name = name; this.age = age; } // Adding methods to prototype Person.prototype.greet = function() { return `Hello, I'm ${this.name}`; }; // Creating objects const person1 = new Person("Alice", 30); // Object literal const person2 = { name: "Bob", age: 25, greet() { return `Hello, I'm ${this.name}`; } }; // Object.create() const person3 = Object.create(Person.prototype); person3.name = "Charlie"; person3.age = 35;

// Creating a Promise const myPromise = new Promise((resolve, reject) => { // Async operation if (success) { resolve(result); } else { reject(error); } }); // Using Promises myPromise .then(result => { console.log(result); return processedResult; }) .catch(error => { console.error(error); }) .finally(() => { console.log("Cleanup"); }); // Promise methods Promise.all([promise1, promise2, promise3]); Promise.allSettled([promise1, promise2, promise3]); Promise.race([promise1, promise2, promise3]); Promise.resolve(value); Promise.reject(reason);

// Async function async function fetchData() { try { const response = await fetch('/api/data'); const data = await response.json(); return data; } catch (error) { console.error('Error:', error); throw error; } } // Using async function fetchData() .then(data => console.log(data)) .catch(error => console.error(error)); // Async arrow function const fetchUser = async (id) => { const response = await fetch(`/api/users/${id}`); return response.json(); }; // Parallel execution async function fetchMultiple() { const [users, posts, comments] = await Promise.all([ fetch('/api/users'), fetch('/api/posts'), fetch('/api/comments') ]); return { users: await users.json(), posts: await posts.json(), comments: await comments.json() }; }

// Basic error handling try { // Code that might throw an error throw new Error("Something went wrong"); } catch (error) { console.error("Error:", error.message); } finally { console.log("This always executes"); } // Specific error types try { JSON.parse(invalidJSON); } catch (error) { if (error instanceof SyntaxError) { console.log("Invalid JSON syntax"); } else if (error instanceof ReferenceError) { console.log("Reference error"); } else { console.log("Unknown error:", error); } } // Custom errors class CustomError extends Error { constructor(message) { super(message); this.name = "CustomError"; } } throw new CustomError("Custom error message");