Object-Oriented Programming: with Prototypes

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Sidenote: Andrew Hedges makes a good point, that there are actually many prototypal languages. It's worth noting that these others exist, but also worth noting that none of them are anything close to mainstream. NewtonScript seemed to have some traction for a while, but died with its platform. It's also possible to extend some modern languages in ways which add prototypal capabilities.

An intro to object-oriented programming in JavaScript: objects, prototypes, and classes

A prototype-based language, does not make the distinction of classes vs objects: it simply has objects. A prototype-based language has the notion of a prototypical object, an object used as a template from which to get the initial properties for a new object. Any object can specify its own properties, either when you create it or at run time.

In addition, any object can be associated as the prototype for another object , allowing the second object to share the first object's properties. Prototype-based programming is a style of object-oriented programming where classes are not present, and behavior reuse or inheritance in class-based languages is performed by cloning existing objects that serve as prototypes. Instead of declaring a class structure, you can create objects of the same type, and add to their definition any time you like using the object's prototype.


  1. Prototypal Object-Oriented Programming using JavaScript – A List Apart.
  2. The Prague cemetery.
  3. A guide to prototype-based class inheritance in JavaScript.

It's more flexible than the normal way of doing things. If you just use objects at runtime instead of a class at compile to build new objects, this opens up the possibility of extending an object without knowing any details about it. Of course, it may become a disadvantage pretty quickly depending on usage. I make no assumptions about the language here, so it is applicable to languages other than javascript which are not as dynamic. You may get the object from just about anywhere; your own code, from the network, from the database, from external linkage and so on.

Note that, a language don't have to implement prototype inheritance like javascript. In javascript, a prototype object is merely shared, so is its properties, among the inheritors. The alternative is copying over all the properties of the prototype to the new object. Each approach has its strengths in different situations. I like the second more but it isn't what javascript does.

Modular Javascript - Prototypal Pattern vs Classical OOP in JS

Use Stack Overflow for Teams at work to find answers in a private and secure environment. Get your first 10 users free. Sign up. Learn more. First 10 Free. What does it mean that Javascript is a prototype based language? Ask Question. Asked 10 years, 11 months ago. Active 1 year, 1 month ago.

Viewed 49k times. One of the major advantages with Javascript is said to be that it is a prototype based language. But what does it mean that Javascript is prototype based, and why is that an advantage? Tom van der Woerdt This rippling effect potentially affects all the subclasses. This sounds like a good idea in theory if you are building a perfectly distributed system but in practice, designing a program consisting of perfectly self-contained objects is hard and limiting.

Lots of real world applications require solving difficult problems with many moving parts.

This article has some interesting points about the design challenges OOP applications:. Yet these behaviors have to live somewhere, so we end up concocting nonsense Doer classes to contain them…And these nonsense entities have a habit of begetting more nonsense entities: when I have umpteen Manager objects, I then need a ManagerManager.

But before we go there, we need to talk about the last cornerstone of OOP:. In OOP, this means designing a class or prototype that can be adapted by objects that need to work with different kinds of data. Suppose to want to create a general polymorphic object that takes some data and a status flag as parameters. If the status says the data is valid i. If the status flags the data as invalid, then the function will not be applied onto the data and the data, along with the invalid status flag, will be returned.

Maybe is a wrapper for data.

Classes vs Prototypes

To wrap the data in Maybe , we provide an additional field called status that indicates if the data is valid or not. We can make Maybe a prototype with a function called apply , which takes a function and applies it on the data only if the status of the data indicates that it is valid. Now we create two objects from the Maybe prototype called Number :.

You will see a runtime error when you uses an undefined method on a data type.

Object-Oriented JavaScript

For example, suppose we try the following:. However, if we used our Number and String objects to wrap the numbers and strings before operating on them, we can prevent these run time errors:. What will the following print out? Since we designed our Maybe prototype to only apply the function onto the data if the data is the right type, this will be logged to console:. Typically this can occur during data retrieval and validation. In Maybe , we are handling the failure in type validation by printing to a string, but we can easily revise the getOrElse function to call another function which handles the validation error.

Some programming languages like Haskell come with a built-in monad type , but in JavaScript, you have to roll your own. ES6 introduced Promise , which is a monad for dealing with latency. Sometimes you need data that could take a while to retrieve. Promise lets you write code that appears synchronous while delaying operation on the data until the data becomes available. Using Promise is a cleaner way of asynchronous programming than using callback functions, which could lead to a phenomenon called the callback hell. JavaScript easily lets us bundle related functions and data together in an object:.

Then we can use the Person object directly like this:. Then we can create an instance of user using Object. A gotcha here is use Object. Objects in JavaScript are mutable so when you straight out assigning to create a new object and you mutate the second object, it will change the original object! Except for numbers, strings, and boolean, everything in JavaScript is an object. Like Lego pieces, we can create copies of the same objects and tweak them, compose them, and pass them onto other objects to augment the capability of other objects.

For example, we define a Customer object with data and functions.

Object Oriented programming in JS - DEV Community 👩‍💻👨‍💻

When our User converts, we want to add the Customer stuff to our user instance. Now we can augment user object with an Customer methods and fields. After running the above two lines of codes, this becomes our user object:. When we want to supply a object with some additional capability, higher order objects cover every use case.

As shown in the example above, we should favor composition over class inheritance because composition is simpler, more expressive, and more flexible :. Classical inheritance creates is-a relationships with restrictive taxonomies, all of which are eventually wrong for new use-cases. But it turns out, we usually employ inheritance for has-a , uses-a , or can-do relationships.

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