Objects and JSON

Objects are the most important data structure in JavaScript. They store collections of key-value pairs and are the foundation of almost everything in the language — from simple data containers to complex class instances.

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Creating Objects

Object Literal

The most common way to create an object:

const person = {
  firstName: "Alice",
  lastName: "Smith",
  age: 30,
  isStudent: false,
};

Rules for Property Names

• Property names (keys) are strings (or Symbols).
• If the key is a valid identifier, quotes are optional.
• If the key contains spaces or special characters, wrap it in quotes:

const obj = {
  "full name": "Alice Smith",
  "data-id": 42,
};

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Accessing Properties

Dot Notation (preferred when key is a valid identifier)

console.log(person.firstName); // "Alice"
console.log(person.age);       // 30

Bracket Notation (required for dynamic keys or special characters)

console.log(person["lastName"]); // "Smith"

const key = "age";
console.log(person[key]); // 30

console.log(obj["full name"]); // "Alice Smith"

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Adding, Modifying, and Deleting Properties

const car = { make: "Toyota" };

// Add a property
car.model = "Camry";
car.year = 2024;

// Modify a property
car.year = 2025;