Object Properties

Learn how JavaScript objects store information using properties and how to access, update, and work with those properties.

What are Object Properties?

An object property is a piece of information stored inside a JavaScript object.

Each property has a name, also called a key, and a corresponding value.

For example, an object representing a student can have properties such as name, age, and course.

Key and Value

In an object, the property name acts as the key and the information stored in that property is its value.

Example: name: "Amit" means name is the property and "Amit" is its value.

JavaScript object properties and key value

JavaScript objects store related information using property names and their corresponding values.

Example of Object Properties

name

Student Name

Stores the name of the student. Example: "Amit"

age

Student Age

Stores the age of the student. Example: 22

course

Course Name

Stores the name of the course. Example: "JavaScript"

city

City

Stores the student's city. Example: "Pune"

Object Property Structure

Object student

→

Property / Key name

→

Value "Amit"

A JavaScript object contains properties, and each property connects a key with its corresponding value.

Example 1: Accessing Properties Using Dot Notation

We can use dot notation to access a property of an object. The object name is followed by a dot and the property name.

let student = {
    name: "Amit",
    age: 22,
    course: "JavaScript"
};

console.log(student.name);
console.log(student.age);

Output: Amit
Output: 22

Example 2: Accessing Properties Using Bracket Notation

We can also access object properties using square brackets. The property name is written inside quotation marks.

let student = {
    name: "Amit",
    course: "JavaScript"
};

console.log(student["name"]);
console.log(student["course"]);

Output: Amit
Output: JavaScript

Example 3: Updating an Object Property

Object properties can be changed after the object has been created. We can assign a new value to the property.

let student = {
    name: "Amit",
    age: 22
};

student.age = 23;

console.log(student.age);

Output: 23

Example 4: Object.keys()

The Object.keys() method returns an array containing the property names of an object.

let student = {
    name: "Amit",
    age: 22,
    course: "JavaScript"
};

console.log(Object.keys(student));

Output: ["name", "age", "course"]

Important Note

Dot Notation and Bracket Notation

Dot notation is commonly used when the property name is known directly.

Bracket notation is useful when the property name needs to be accessed dynamically or contains characters that cannot be used with dot notation.

Summary

JavaScript object properties store information using key-value pairs. Properties can be accessed using dot notation or bracket notation, updated by assigning a new value, and listed using Object.keys().