Simple JavaScript Inheritance: What You Need to Know

Simple JavaScript Inheritance: What You Need to Know

A lot of my friends are
C# or C++ developers. They are used to using inheritance in their projects, and when they want to learn or discover JavaScript, one of the first
questions they ask is: “But how can I do inheritance with JavaScript?”

Actually, JavaScript uses
a different approach than C# or C++ to create an object-oriented language. It
is a prototype-based language. The concept of prototyping implies that
behavior can be reused by cloning existing objects that serve as
prototypes. Every object in JavaScript depends on a prototype which defines a
set of functions and members that the object can use. There is no class—just
objects. Every object can then be used as prototype for another object.

This concept is extremely
flexible, and we can use it to simulate some concepts from OOP, like inheritance.

Implementing Inheritance

Let’s look at what we want
to create with this hierarchy using JavaScript:

Inheritance in JavaScript

First of all, we can
create ClassA easily. Because there are no explicit classes, we can define a set
of behavior (A class so…) by just creating a function like this:

This “class” can be
instantiated using the new keyword:

And to use it using our

Fairly simple,

The complete sample is
just eight lines long:

Now let’s add a tool to
create “inheritance” between classes. This tool will just have to do one single
thing: clone the prototype.

This is exactly where
the magic happens! By cloning the prototype, we transfer all members and
functions to the new class.

So if we want to add a
second class that will be child of the first one, we just have to use this

Then because ClassB
inherited the print function from ClassA, the following code is

And produces the
following output:

We can even override the print
function for ClassB:

In this case, the
produced output will look like this:

The trick here is to call
ClassA.prototype to get the base print function. Then thanks to the call
function we can call the base function on the current object (this).

Creating ClassC is
now obvious:

And the output is:

More Hands-On With

It might surprise you a bit, but Microsoft
has a bunch of free learning on many open source JavaScript topics, and we’re on
a mission to create a lot more with Microsoft Edge. Check out my own:

Or our team’s learning series:

And some free tools: Visual Studio Community, Azure Trial, and cross-browser testing tools for Mac, Linux, or Windows.

And Some Philosophy…

To conclude, I just want to clearly state
that JavaScript is not C# or C++. It has its own philosophy. If you are
a C++ or C# developer and you really want to embrace the full power of
JavaScript, the best tip I can give you is: Do not try to replicate your
language into JavaScript. There is no best or worst language. Just different

This article is part of the web dev tech
series from Microsoft. We’re excited to share
Microsoft Edge and the new EdgeHTML rendering engine with you. Get free
virtual machines or test remotely on your Mac, iOS, Android, or Windows device

Source: Tuts Plus

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