JavaScript

In JavaScript, objects are collections of properties, where each property is a key-value pair. Properties define the characteristics and behavior of objects.

---

🔑 What Is a Property?

A property is an association between a key (name) and a value.

const person = {
  name: "Alice",   // 'name' is a property with the value "Alice"
  age: 25
};

• name and age are keys (also called property names).
• "Alice" and 25 are the values associated with those keys.

---

📦 Property Types

There are two main types of object properties:

1. Data Properties

These store values (like strings, numbers, objects, etc.)

const user = {
  username: "devin",
  score: 100
};

2. Accessor Properties

These are defined using getters and setters.

const profile = {
  firstName: "John",
  lastName: "Doe",
  get fullName() {
    return `${this.firstName} ${this.lastName}`;
  }
};

console.log(profile.fullName); // John Doe

---

🛠 Ways to Access Object Properties

1. Dot Notation

console.log(person.name); // "Alice"

2. Bracket Notation

console.log(person["name"]); // "Alice"

🔔 Use bracket notation when the property name is dynamic or contains special characters.

---

➕ Adding and Updating Properties

person.location = "USA"; // Add new
person.age = 30;         // Update existing

---

❌ Deleting Properties

delete person.age; // Removes the 'age' property

---

🔍 Checking Property Existence

Using in operator

"name" in person; // true

Using hasOwnProperty()

person.hasOwnProperty("name"); // true

---

🧮 Enumerating Object Properties

Object.keys()

Returns an array of keys.

Object.keys(person); // ["name", "location"]

Object.values()

Returns an array of values.

Object.values(person); // ["Alice", "USA"]

Object.entries()

Returns an array of key-value pairs.

Object.entries(person); // [["name", "Alice"], ["location", "USA"]]

---

🧰 Property Descriptors

Each property in an object has attributes that control its behavior:

• writable: Can be changed.
• enumerable: Shows up in loops.
• configurable: Can be deleted or modified.

You can define properties more precisely with Object.defineProperty():

Object.defineProperty(person, "gender", {
  value: "female",
  writable: false,
  enumerable: true,
  configurable: false
});

---

🧼 Best Practices

• Use dot notation for readability.
• Use bracket notation for dynamic keys.
• Avoid overwriting built-in object properties.
• Use const when declaring objects (you can still change properties).

---