Course Overview

Overview of history of the JavaScript language

History of JavaScript

Overview of the relationship between JavaScript and Java

JavaScript vs Java

Overview of how JavaScript is evolved as a programming language

How is it evolved?

Overview of how we can track upcoming features in the JavaScript language

How to track upcoming features?

Overview of how the ECMAScript is versioned

How is ECMAScript versioned?

Explanation of whether JavaScript is interpreted or a compiled language

Is it interpreted or compiled?

Explanation of how JavaScript is executed

How is it executed?

Execution Context

Explanation of what is a callstack and how it is used in JavaScript

Callstack

Overview of memory management in JavaScript

Memory

What is JavaScript

What is hoisting?

Explanation of common misconception about hoisting in JavaScript

Misconception about hoisting

Hoisting

What is scope?

Explanation of global scope in JavaScript

Global scope

Explanation of function scope in JavaScript

Function scope

Block scope

Explanation of module scope in JavaScript

Module scope

Scope chain

Scope

What is coercion?

Diving into inner details of  coercion in JavaScript

Deeper look at coercion

Explanation of what abstract operations are and common types of abstract operations in JavaScript

Abstract operations

Explanation of how abstract or loose equality works in JavaScript

Abstract equality operator

Explanation of how the addition operator works in JavaScript

Addition operator

Explanation of how relational operators work in JavaScript

Relational operators

Coercion exercise for testing and practicing the knowledge learned in this module

Coercion exercise

Coercion

What is a closure?

Explanation of a common misconception about closures in JavaScript

Misconception about closures

Explanation of the problem of closures inside loops and how to fix it

Closures inside loops

Explanation of closures can be used to hide data

Data hiding using closures

Closures

What is prototypal inheritance?

Prototype chain

__proto__ property

Explanation of how we can create objects with custom prototypes in JavaScript

Custom prototypes

Explanation of how prototype chain is set with ES6 classes

ES6 classes and prototypes

Prototypes

Explanation of this keyword in JavaScript

What is this?

Explanation of how "this" works inside arrow functions

Arrow functions and "this"

Explanation of how value of "this" can be set explicitly

Explicitly binding "this"

globalThis

Summarizing "this"

'this' keyword

What is a symbol?

Explanation of why symbols were added in JavaScript

Why symbols?

Symbols and privacy

Explanation of global symbols in JavaScript

Global symbols

Explanation of what well-known symbols are in JavaScript

Well-known symbols

Symbol

Overview of asynchronous behavior of JavaScript

Overview

Overview of how callbacks help us write asynchronous code in JavaScript

Callbacks

Event loop

Promise

Explanation of promise chaining in JavaScript

Promise chaining

Explanation of some static methods of promises and their use cases

Use cases for static Promise methods

Explanation of async-await syntax in JavaScript

async await

Explanation of microtasks, how they are processed, and how they are linked to promises

Microtasks

Explanation of common anti-patterns to avoid when using promises in JavaScript

Promise anti-patterns

Asynchronous JavaScript

Explanation of what is an iterator in JavaScript

Iterators

Explanation of what is a generator in JavaScript

Generators

Explanation of how we can create asynchronous iterators in JavaScript

Asynchronous iterators

Explanation of how we can create asynchronous generators in JavaScript

Asynchronous generators

Iterators and Generators

Overview of what is debugging and different ways to debug JavaScript

Debugging

Overview of using the "debugger" statement to debug JavaScript

Debugger statement

Overview of using the breakpoints in browser developers' tools to debug JavaScript

Breakpoints in browser

Overview of using the VS Code debugger to debug JavaScript

VS Code debugger

Debugging JavaScript

Final thoughts and advice regarding how to continue the exciting journey of learning JavaScript

Conclusion

Wrap up

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Become a confident JavaScript pro by unraveling the most challenging aspects of the language. With easy-to-understand explanations and code examples, you’ll gain a deeper and solid understanding of JavaScript's most complex features.

Advanced JavaScript Unleashed is for beginner and intermediate developers alike, who want to elevate their JavaScript skills and become senior engineers by gaining a deeper understanding of the core topics of the language.

Advanced JavaScript Unleashed

 is a general object-oriented programming concept allowing objects to inherit other objects' methods and properties. This reduces code duplication and promotes code sharing between different objects.

Unlike traditional object-oriented programming languages like Java or C#, JavaScript has a different way of dealing with inheritance. Objects in JavaScript are 

 to other objects, and this linkage allows an object to use the functionality of another object to which it is linked.

The linkage between objects in JavaScript forms a chain. This chain is known as the "

". Think of the scope chain, where each scope is linked to another scope until we reach the global scope. The prototype chain is similar: one object is linked to another object. This other object, in turn, is linked to another object, forming a chain between objects.

The prototype chain allows the sharing of properties between objects, and this is the idea of inheritance in JavaScript, known as the "

". In prototypal inheritance, an object from which other objects inherit properties is known as the "

When we create an object literal in JavaScript, it is, by default, linked to the built-in 

Objects in JavaScript have a hidden internal slot named 

. When an object is created, it is linked to another object by saving a reference to the other object in the 

 internal slot of the newly created object. The other object whose reference is saved in the internal slot will serve as the "prototype" of the newly created object.

 is linked to and inherits the properties. But as 

 is an internal slot not accessible by JavaScript, later in this lesson, we will see how we can access the prototype of any object.

In our discussion of prototypal inheritance so far, you might have noticed the term "prototype" used in two different contexts: one as a property, i.e., 

 and the other as a general term used to describe an object that shares its properties with another object. This clash of names creates confusion among many when they first start learning about prototypal inheritance in JavaScript.

As functions are objects in JavaScript, they can have properties just like any other object. The property name "prototype" is one of the functions' properties. The arrow functions do not have this property.

The prototype property of a function refers to an object that is used as the "prototype" of other objects when that function is invoked as a "constructor function" using the "new" keyword. Again, the term "prototype" has been used in two contexts here:

The following code example shows that the property named "prototype" exists on functions:

---
title: What is prototypal inheritance?
description: Explanation of prototypal inheritance
isPublicLesson: false
useMdx: true
code: https://gitlab.com/fullstackio/books/newline-course-apps/advanced-javascript-unleashed-app/-/tree/main/module_06/lesson_06.01
---

**Inheritance** is a general object-oriented programming concept allowing objects to inherit other objects' methods and properties. This reduces code duplication and promotes code sharing between different objects.

Unlike traditional object-oriented programming languages like Java or C#, JavaScript has a different way of dealing with inheritance. Objects in JavaScript are _linked_ to other objects, and this linkage allows an object to use the functionality of another object to which it is linked.

The linkage between objects in JavaScript forms a chain. This chain is known as the "**prototype chain**". Think of the scope chain, where each scope is linked to another scope until we reach the global scope. The prototype chain is similar: one object is linked to another object. This other object, in turn, is linked to another object, forming a chain between objects.

The prototype chain allows the sharing of properties between objects, and this is the idea of inheritance in JavaScript, known as the "**prototypal inheritance**". In prototypal inheritance, an object from which other objects inherit properties is known as the "**prototype**" of those objects.

When we create an object literal in JavaScript, it is, by default, linked to the built-in `Object.prototype` object.

```js
const obj = {};
```

The `Object.prototype` object is the **prototype** of the `obj` object in the code example above.

## How are objects linked?

Objects in JavaScript have a hidden internal slot named `[[Prototype]]`. When an object is created, it is linked to another object by saving a reference to the other object in the `[[Prototype]]` internal slot of the newly created object. The other object whose reference is saved in the internal slot will serve as the "prototype" of the newly created object.

In the code example above, the `[[Prototype]]` slot of the `obj` object contains a reference to the `Object.prototype` object. So, `obj.[[Prototype]]` gives us the prototype of the `obj` object, the object from which `obj` is linked to and inherits the properties. But as `[[Prototype]]` is an internal slot not accessible by JavaScript, later in this lesson, we will see how we can access the prototype of any object.

## The "prototype" property

In our discussion of prototypal inheritance so far, you might have noticed the term "prototype" used in two different contexts: one as a property, i.e., `Object.prototype` and the other as a general term used to describe an object that shares its properties with another object. This clash of names creates confusion among many when they first start learning about prototypal inheritance in JavaScript.

As functions are objects in JavaScript, they can have properties just like any other object. The property name "prototype" is one of the functions' properties. The arrow functions do not have this property.