JavaScript Object Properties

Accessing Properties

person.name
person.age

person["name"]
person["age"]

let prop = "name";
person[prop]

person.email = "[email protected]";
person["phone"] = "123-456-7890";

🔹 Dot vs Bracket Notation

Both methods access the same properties, but have different use cases:

let car = {
    brand: "Honda",
    model: "Civic",
    year: 2022,
    "fuel-type": "gasoline"  // property with hyphen
};

// Dot notation (preferred for simple names)
console.log(car.brand);    // "Honda"
console.log(car.model);    // "Civic"

// Bracket notation (required for special characters)
console.log(car["fuel-type"]);  // "gasoline"
console.log(car["year"]);       // 2022

// Dynamic property access
let property = "brand";
console.log(car[property]);     // "Honda"

🔹 Adding and Modifying Properties

You can add new properties or change existing ones:

let student = {
    name: "Emma",
    grade: "A"
};

// Add new properties
student.age = 19;
student.major = "Computer Science";
student["graduation-year"] = 2025;

// Modify existing properties
student.grade = "A+";

console.log(student);
// Output: {name: "Emma", grade: "A+", age: 19, major: "Computer Science", graduation-year: 2025}

🔹 Deleting Properties

Use the delete operator to remove properties:

let product = {
    name: "Laptop",
    price: 999,
    category: "Electronics",
    inStock: true
};

// Delete a property
delete product.inStock;
delete product["category"];

console.log(product);
// Output: {name: "Laptop", price: 999}

console.log(product.inStock);  // undefined

🔹 Checking if Properties Exist

Several ways to check if a property exists in an object:

let book = {
    title: "JavaScript Basics",
    author: "Jane Doe",
    pages: 250
};

// Using 'in' operator
console.log("title" in book);        // true
console.log("publisher" in book);    // false

// Using hasOwnProperty()
console.log(book.hasOwnProperty("author"));    // true
console.log(book.hasOwnProperty("isbn"));      // false

// Checking if property is undefined
console.log(book.title !== undefined);        // true
console.log(book.publisher !== undefined);    // false

🔹 Looping Through Properties

Use for...in loop to iterate through object properties:

let animal = {
    name: "Lion",
    species: "Panthera leo",
    habitat: "Savanna",
    diet: "Carnivore"
};

// Loop through all properties
for (let property in animal) {
    console.log(property + ": " + animal[property]);
}

// Get all property names
console.log(Object.keys(animal));
// Output: ["name", "species", "habitat", "diet"]

// Get all property values
console.log(Object.values(animal));
// Output: ["Lion", "Panthera leo", "Savanna", "Carnivore"]