Working with
Objects: Properties and Methods

What is an Object in JavaScript?

In JavaScript, an object is a collection of key-value pairs. Each key is called a property, and if the value is a function, it's called a method.

Creating an Object

You can create an object using curly braces {} and define properties inside it.

const person = {
  name: "Alice",
  age: 25,
  isStudent: true
};
console.log(person);
    

Output:

{ name: 'Alice', age: 25, isStudent: true }
    

Accessing Object Properties

There are two ways to access properties: dot notation and bracket notation.

console.log(person.name);       // Dot notation
console.log(person["age"]);     // Bracket notation
    

Output:

Alice
25
    

Adding and Updating Properties

You can add or update properties at any time using assignment.

person.city = "New York";       // Adding
person.age = 26;                // Updating
console.log(person);
    

Output:

{ name: 'Alice', age: 26, isStudent: true, city: 'New York' }
    

Deleting Properties

You can remove a property using the delete keyword.

delete person.isStudent;
console.log(person);
    

Output:

{ name: 'Alice', age: 26, city: 'New York' }
    

What is a Method in JavaScript?

A method is a function inside an object. It defines behavior related to that object.

Defining Methods

const user = {
  name: "Bob",
  greet: function() {
    return "Hello, " + this.name + "!";
  }
};

console.log(user.greet());
    

Output:

Hello, Bob!
    

Why use this?

The this keyword refers to the current object. Inside a method, this lets you access other properties of the same object.

ES6 Shorthand for Methods

From ES6 onwards, you can define methods in a shorter way:

const calculator = {
  add(a, b) {
    return a + b;
  },
  subtract(a, b) {
    return a - b;
  }
};

console.log(calculator.add(5, 3));
console.log(calculator.subtract(10, 4));
    

Output:

8
6
    

Can an object hold both data and behavior?

Yes! This is the core of Object-Oriented Programming (OOP). Objects group related data (properties) and behavior (methods).

Example: Complete Object with Multiple Methods

const car = {
  brand: "Toyota",
  model: "Camry",
  year: 2020,
  getDetails() {
    return this.brand + " " + this.model + " (" + this.year + ")";
  },
  isNew() {
    return this.year >= 2022;
  }
};

console.log(car.getDetails());
console.log("Is new car:", car.isNew());
    

Output:

Toyota Camry (2020)
Is new car: false
    

Questions You Might Ask

Q: Can we store arrays and other objects as property values?

A: Yes! JavaScript objects can hold any data type, including arrays, functions, and other objects.

const student = {
  name: "John",
  subjects: ["Math", "Science"],
  address: {
    city: "Delhi",
    zip: 110001
  }
};

console.log(student.subjects[0]);       // Math
console.log(student.address.city);      // Delhi
    

Output:

Math
Delhi
    

Summary

• Objects group related data and functions.
• Properties are key-value pairs inside an object.
• Methods are functions defined as values of properties.
• this refers to the current object inside a method.