---
title: "Differences between instance properties and prototype properties in JavaScript objects."  
description: "Differences between instance properties and prototype properties in JavaScript objects."  
author: "Utpal Vishwas"  
published: 2023-10-08  
updated: 2023-10-09  
canonical: https://www.mindstick.com/forum/160068/differences-between-instance-properties-and-prototype-properties-in-javascript-objects  
category: "javascript"  
tags: ["javascript", "oops"]  
reading_time: 2 minutes  

---

# Differences between instance properties and prototype properties in JavaScript objects.

[Differences](https://www.mindstick.com/articles/12918/cat-5e-vs-cat-6a-understanding-the-major-differences) between [instance](https://www.mindstick.com/forum/155658/testing-connection-to-cloud-sql-instance-with-a-mysql-client-from-vm-instance) [properties](https://www.mindstick.com/articles/23331/nootropics-7-different-types-and-their-unique-properties) and [prototype](https://www.mindstick.com/news/2386/every-detail-regarding-twitter-leak-of-xiaomi-outfolding-smartphone-prototype) properties in [JavaScript](https://www.mindstick.com/articles/874/how-to-create-watermark-text-for-textbox-by-using-javascript) objects.

## Replies

### Reply by Aryan Kumar

In JavaScript, objects can have instance properties and prototype properties, and understanding the differences between them is crucial for effective object-oriented programming. These two types of properties serve different purposes and have different characteristics:

## Instance Properties:

- **Per-Object Basis:** Each instance of an object has its own set of instance properties. These properties are specific to each individual object created from a constructor or a class.
- **Defined in the Constructor:** Instance properties are defined within the constructor function or the class constructor using the **this** keyword.
- **Memory Consumption:** Since each instance has its own copy of instance properties, they consume memory separately for each object.

```plaintext
function Person(name) {
  this.name = name; // Instance property
}

const person1 = new Person("Alice");
const person2 = new Person("Bob");

console.log(person1.name); // "Alice"
console.log(person2.name); // "Bob"
```

## Prototype Properties:

- **Shared Across Instances:** Prototype properties are shared among all instances of an object created from the same constructor or class. They are stored in the object's prototype, and changes to them affect all instances.
- **Defined Outside the Constructor:** Prototype properties are typically defined outside the constructor, often using the prototype chain. This promotes memory efficiency as they are not duplicated for each instance.
- **Memory Efficiency:** Since prototype properties are shared, they are memory-efficient when you have many instances of the same object type.

```plaintext
function Person(name) {
  this.name = name; // Instance property
}

Person.prototype.sayHello = function() {
  console.log(`Hello, my name is ${this.name}`);
};

const person1 = new Person("Alice");
const person2 = new Person("Bob");

person1.sayHello(); // "Hello, my name is Alice"
person2.sayHello(); // "Hello, my name is Bob"
```

In summary, instance properties are specific to individual instances of an object, while prototype properties are shared among all instances created from the same constructor or class. Prototype properties are often used for methods or properties that are common to all instances to save memory and promote code efficiency. Understanding when and how to use each type of property is essential for effective JavaScript object-oriented programming.


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