Editing JavaScript (section)

==== Prototypes ====
{{Main|Prototype-based programming}}

JavaScript uses [[prototype-based programming|prototypes]] where many other object-oriented languages use [[Class (computer science)|classes]] for [[Inheritance (object-oriented programming)|inheritance]],<ref>{{cite web|title=Inheritance and the prototype chain|url=https://developer.mozilla.org/en-US/docs/JavaScript/Guide/Inheritance_and_the_prototype_chain|work=[[Mozilla]] Developer Network |access-date=April 6, 2013|archive-date=April 25, 2013|archive-url=https://web.archive.org/web/20130425144207/https://developer.mozilla.org/en-US/docs/JavaScript/Guide/Inheritance_and_the_prototype_chain|url-status=live}}</ref> but it's still possible to simulate most class-based features with the prototype system.<ref>{{cite book|last=Herman|first=David|title=Effective JavaScript|year=2013|publisher=Addison-Wesley|isbn=978-0-321-81218-6|page=83 |url=https://books.google.com/books?id=Nz9iAwAAQBAJ&pg=PA83 }}</ref> Additionally, [[ECMAScript |ECMAScript version 6]] (released June 2015) introduced the keywords '''class''', '''extends''' and '''super''', which serve as syntactic sugar to abstract the underlying prototypal inheritance system with a more conventional interface. Constructors are declared by specifying a method named '''constructor''', and all classes are automatically subclasses of the base class Object, similarly to Java. <syntaxhighlight lang="javascript">
class Person {
    constructor(name) {
        this.name = name;
    }
}

class Student extends Person {
    constructor(name, id) {
        super(name);
        this.id = id;
    }
}

const bob = new Student("Robert", 12345);
console.log(bob.name); // Robert
</syntaxhighlight>Though the underlying object mechanism is still based on prototypes, the newer syntax is similar to other object oriented languages. Private variables are declared by prefixing the field name with a [[number sign]] (#), and [[Polymorphism (computer science)|polymorphism]] is not directly supported, although it can be emulated by manually calling different functions depending on the number and type of arguments provided.<ref name="JavaScriptNext">{{cite book |last=Ghandi |first=Raju |date=2019 |title=JavaScript Next|location=New York City |publisher=Apress Media |pages=159–171 |isbn=978-1-4842-5394-6}}</ref>