JavaScript Objects: Properties and Methods

Understand JavaScript objects, properties, methods, dot notation and bracket notation with beginner-friendly examples.

Describe a value with properties

An object groups related information using named properties. This example describes one book:

const book = {
  title: "Small Web Projects",
  pages: 180,
  available: true
};

Read and update properties

Use dot notation when the property name is known in your code. Bracket notation is useful when the property name is stored in a variable.

console.log(book.title);
book.available = false;

const field = "pages";
console.log(book[field]);

Add a method

A method is a function stored as an object property. It can use this to refer to the object that owns it.

const user = {
  name: "Sam",
  greet() {
    return `Hello, ${this.name}`;
  }
};

Create an updated object without changing the original

The spread syntax copies an object’s own enumerable properties into a new object. Put a changed property after the spread to replace its old value in the copy:

const updatedBook = {
  ...book,
  available: false
};

This is a shallow copy: nested objects are still shared references. For simple flat objects, the pattern is a convenient way to preserve the original while creating an updated version.

Object questions

Can a const object be changed?

const prevents assigning a different object to the same variable. It does not freeze the object, so its properties can still be updated unless the object is frozen separately.

When should I use an object instead of an array?

Use an object when values have descriptive names, such as a book’s title and page count. Use an array when you need an ordered collection of values, such as a list of book titles.