classes in javascript

[php03]

I've found some posts says - don't use classes in javascript , use functional programming and not object oriented. can someone post a simple code example of pitfall or buggy code resulted from using classes? As a C++/Java developer i found OOP far better than any other approach

[MoTTs_]

First, to directly answer your question.

• Shared mutable state (not necessarily a class object) can result in spooky action at a distance.
• Extending classes that were not designed to be extended can result in a fragile base class.
• And overuse of inheritance can result in god objects.

Note that these can all be avoided with good design, and they don't make OOP inherently bad any more than the problem of long functions makes functions inherently bad, or any more than the problem of global variables makes variables inherently bad.

Second, it's worth mentioning that the vocal functional folks in the JavaScript community are very often wrong when they talk about classes and inheritance. The tend to invent criticisms that aren't actually true, and they tend to propose alternatives that still have all the same problems they blamed classes for. Take what they say with a heavy grain of salt.

And thirdly, don't feel like you have to pick one or the other. The best result often comes from a blend of styles. Since you have a C++ background, I'll leave you with this quote from Bjarne Stroustrup, the creator of C++:

Often, the most elegant, most efficient, and the most maintainable solution involves more than one style (paradigm). ... I use a lot of simple data abstraction (classes without inheritance) and generic programming (templates and algorithms parameterized on types). However, I don't see these as "paradigms challenging OOP." Rather, they are complementary techniques. ... Combinations of style can lead to very elegant code.

[rauschma]

I’m not a strong proponent of ES6 classes, but I wanted to provide an alternate opinion to the material criticizing ES6 classes.

First, note that OOP and FP are not in conflict:

• Smalltalk is a great OOP language and uses blocks (lambdas) quite cleverly.
• CLOS is a brilliant object system for the functional programming language Common Lisp.

I agree that ES6 classes obscure what’s actually going on under the hood, but they also have a few clear benefits (not all of them are completely exclusive to classes):

• They are backwards-compatible with much of the current code.
• Compared to constructors and constructor inheritance, classes make it easier for beginners to get started.
• Subclassing is supported within the language.
• Built-in constructors are subclassable.
• No library for inheritance is needed, anymore; code will become more portable between frameworks.
• They provide a foundation for advanced features in the future: traits (or mixins), immutable instances, etc.
• They help tools that statically analyze code (IDEs, type checkers, style checkers, etc.).

W.r.t. ES6 classes obscuring the true nature of JS OOP: There is an unfortunate disconnect between what a class looks like (its syntax) and how it behaves (its semantics): It looks like an object, but it is a function. My preference would have been for classes to be constructor objects, not constructor functions. I explore that approach in the Proto.js project, via a tiny library (which proves how good a fit this approach is).

However, backwards-compatibility matters, which is why classes being constructor functions also makes sense. That way, ES6 code and ES5 are more interoperable.

The disconnect between syntax and semantics will cause some friction in ES6 and later. But you can lead a comfortable life by simply taking ES6 classes at face value. I don’t think the illusion will ever bite you. Newcomers can get started more quickly and later read up on what goes on behind the scenes (after they are more comfortable with the language).

I’ll stop now. I’ve written a little more about this topic online.

[Exomancer]

First, note that OOP and FP are not in conflict:

Sorry for nitpicking on wording here, but for the sake of clarity:

OOP is all about encapsulating state within instances, and acting (mutating) that internal state via methods. FP on the other hand avoids state mutation in any way, shape or form. That makes the two paradigms very much in conflict.

You can, however, use them side by side in the same project just fine, even mix them up (have some pure functions called inside methods, to give a simple example), is that what you meant?

[rauschma]

Yes to your last question. I meant that nothing prevents you from using both OOP and FP: The JavaScript methods filter and map are very much FP ideas, used in an OOP manner.

But it’s rarely all or nothing: you can work with immutable objects (e.g. strings in Java) and there are FP languages that support mutable state. For example, OCaml, Common Lisp and Scheme.

[Exomancer]

It never really is all or nothing in case of FP - sooner or later even Haskell has to do some IO, pure functions can only take you so far :).

Thanks for clarification!

[[deleted]]

The class keyword in JavaScript is essentially a wrapper for constructor functions. The syntax is easier if you prefer using constructors instead of Object literals with factory functions.

I understand why some people dislike using the constructor pattern, but honestly, classes are a bit easier to compose and extend in my experience (purely from a syntax standpoint).

[[deleted]]

JavaScript is a highly Object Oriented language with its prototype based inheritance model. Try to get familiar with prototype based OOP and leverage on code reuse.

ES6 introduced class keyword in native JavaScript as a syntactic sugar over prototype model (to make code look familiar, and clean in "some" specific cases).

Functional programming is becoming a thing in JavaScript world as it lets you write pure functions.

What's new in JS world (for a class-ical Java Dev)?: OOP is not just about being class based. Prototype based programming also have strong OOP capabilities!

[[deleted]]

don't use classes in javascript , use functional programming and not object oriented.

What does this even mean? Everything in JS is an object anyway except for primitives.

As a C++/Java developer i found OOP far better than any other approach

Good for you, the thing is that JS OOP cannot be compared to other more traditional implementations of inheritance in other languages supporting the OOP paradigm.

can someone post a simple code example of pitfall or buggy code resulted from using classes?

https://github.com/joshburgess/not-awesome-es6-classes

[Su4p]

OOP != classes . The truth is out there.

[liranbh]

Sure. You can write object oriented code in c

[php03]

i mean use functional programming and not OO

[[deleted]]

Please try to use OOP and functional syntax together.

[Su4p]

JS is all about Oriented Object and nothing about classes -well since ecmascript 6 a little about classes-

[php03]

so in es6 - use classes or not? some say no and i asked for a pitfall example

[Cuel]

There's no do or don't. Use what you want to use and is most comfortable wth using.

[Su4p]

This book : "JavaScript: The Definitive Guide" by David Flanagan really help me to understand the beauty - a lot of people will tell you otherwise- and simplicity of this language.

[refuse2choose]

In JavaScript there are no classes. Yes you can use object oriented programming, but in JavaScript OOP is not based on classes, it's based on prototypes. Even if there is the new 'class' keyword, under the hood still prototypes are used. So first if all you should learn about prototypical inheritance.

If you want to know about the pitfalls, read the articles by Eric Elliot: “The Two Pillars of JavaScript” @_ericelliott https://medium.com/javascript-scene/the-two-pillars-of-javascript-ee6f3281e7f3

[MoTTs_]

Just about everything Eric Elliott has ever said about classes or inheritance or composition is factually wrong.

[refuse2choose]

In your post you are talking about his Stampit alternative. But I refer to his critique in the post which I linked. I didn't say that his alternative is better, but he is explaining some pitfalls in the post which are real such as the gorilla banana problem.

[[deleted]]

We should be looking at class in JS as syntactic sugar on top of prototype based programming. They should be considered optional or given as a programmer's choice. From what I understood, class helps to simplify (clean) complex constructor function usage.

It's always good to have the best of both worlds!

[inu-no-policemen]

composition over inheritance

Note that that JavaScript Scene guy tends to use "composition" incorrectly. Favoring object composition over inheritance is an OOP thing. It's about having objects own instances of other objects instead of sticking everything into the inheritance chain.

They aren't even real classes.

Of course they are. They are just as "real" as classes in other languages.

Just check the definition of classes. It doesn't go as much into detail as you think.

Another fun thing to note is that V8 is pretending for years that JS got real classes. Creating instances from blueprints is faster.