Objects, `Map`, `Set`, `Date` & RegExp

🟡 Intermediate

📖 Definition

Object: Key-value data structure where keys are strings or symbols.
Map: Key-value collection where keys can be any data type (objects, functions, primitives) and insertion order is preserved.
Set: Collection of unique values where duplicates are automatically removed.
Date: Built-in object for managing timestamps, dates, and time calculations.
RegExp: Regular Expressions used for text pattern matching and string validation.

🇮🇳 Hindi

Objects JavaScript ke fundamental building blocks hain. Structured key-value data ke liye Object aur Map use karein, unique items store karne ke liye Set, calendar dates ke liye Date, aur string validations ke liye RegExp ka use hota hai.

🚩 Marathi

Objects madhye data key-value pair स्वरूपात saathavla jato. Duplicate values kadhnyasathi Set cha wapar kara, badalnaraya keys sathi Map, tareekh ani vele sathi Date aani validation sathi RegExp cha wapar kara.

📝 Structures & Features

1. Objects (Dot vs Bracket Notation)

const userProfile = {
  id: 101,
  fullName: "Ananya Roy",
  role: "Engineer",
  skills: ["JS", "React"],
  greet() {
    return `Hi, I am ${this.fullName}`;
  }
};

console.log(userProfile.fullName);       // Dot notation
console.log(userProfile["role"]);        // Bracket notation

// Utility methods
console.log(Object.keys(userProfile));   // ['id', 'fullName', 'role', 'skills', 'greet']
console.log(Object.values(userProfile)); // [101, 'Ananya Roy', 'Engineer', ...]

2. `Set` (Collection of Unique Values)

const numbers = [10, 20, 10, 30, 20, 40];
const uniqueNumbers = new Set(numbers);
uniqueNumbers.add(50);

console.log("Unique Size:", uniqueNumbers.size); // 5 (Duplicates ignored)
console.log("Has 20?", uniqueNumbers.has(20));    // true

3. `Map` (Any Data Type as Key)

const userRoles = new Map();
const keyObject = { id: 1 };

userRoles.set(keyObject, "Administrator");
console.log(userRoles.get(keyObject)); // "Administrator"

4. `Date` Object

const now = new Date();
console.log("Current Year:", now.getFullYear());
console.log("ISO Format:", now.toISOString());

5. Regular Expressions (`RegExp`)

const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
console.log(emailRegex.test("user@domain.com")); // true
console.log(emailRegex.test("invalid-email"));   // false

💡 Complete Example

// Clean user input by removing duplicate tags and validating email
function processUserRegistration(emailInput, tagsArray) {
  const emailPattern = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
  const isValidEmail = emailPattern.test(emailInput);

  const cleanTags = Array.from(new Set(tagsArray));

  return {
    email: emailInput,
    valid: isValidEmail,
    tags: cleanTags,
    registeredAt: new Date().toLocaleDateString()
  };
}

let result = processUserRegistration("dev@example.com", ["js", "html", "js", "css", "html"]);
console.log(result);

👀 Output

{
  email: 'dev@example.com',
  valid: true,
  tags: [ 'js', 'html', 'css' ],
  registeredAt: '9/24/2026'
}

🧪 Try It Yourself

Create an object car with make, model, year, and a drive() method.
Create an array containing numbers with duplicates and convert it to a Set to remove duplicates.

⚠️ Common Mistakes

Forgetting that months in JavaScript Date object are 0-indexed (0 = January, 11 = December!).
Accessing Map entries with dot notation (map.key) instead of using .get(key).

🌍 Real-World Usage

Managing user profile state, filtering unique tags/categories in e-commerce, formatting timestamps, and validating email/password fields in registration forms.

💡 Remember

Use Object for fixed structured records, Set for deduplication, Map when keys are dynamic or non-strings, and Date for calendar tracking.

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Objects, Map, Set, Date & RegExp