Inheriting static properties in Javascript

Question

The design pattern I use in my current project is:

var MyConstructor = function() { ... };
MyConstructor.STATIC_PROPERTY = 'static';

Now if i want to inherit from MyConstructor class, I'd do:

var ChildClass = function() { ... };
ChildClass.prototype = new MyConstructor(); // Or Object.create(...)
ChildClass.prototype.constructor = ChildClass;

Problem is ChildClass.STATIC_PROPERTY is undefined / not inherited ...

Is there a way to fix that?

Secondary question:

If I console.log(MyConstructor), I'd get function() { ...} and nothing about MyConstructor.STATIC_PROPERTY when it's actually there. Where is that STATIC_PROPERTY stored in the end? How can I check/display it?

"Static" properties are simply properties on the constructor function objects. They don't have anything to do with the JavaScript inheritance scheme. — Pointy
– Pointy, Commented Sep 25, 2019 at 14:48
Try console.dir(MyConstructor) to see the static properties. — Pointy
– Pointy, Commented Sep 25, 2019 at 14:49
Since you have access to MyConstructor() in the scope where you define ChildClass, something like ChildClass.STATIC_PROPERTY = MyConstructor.STATIC_PROPERTY should work. ( but might not be desirable ) As stated, it has nothing to do with prototypal inheritance. Nether is it static without using Object.defineProperty() or it's alternatives. We can overwrite it all we want. — Shilly
– Shilly, Commented Sep 25, 2019 at 15:02
Possible duplicate of How to inherit static methods from base class in JavaScript? — ponury-kostek
– ponury-kostek, Commented Sep 25, 2019 at 15:25

Bergi · Accepted Answer · 2019-09-25 19:44:56Z

3

Use an ES6 class, which does prototypically inherit from the parent class (constructor function object):

function MyConstructor() { /* … */ }
MyConstructor.STATIC_PROPERTY = 'static';

class ChildClass extends MyConstructor { /* … */ }
console.log(ChildClass.STATIC_PROPERTY);

The alternative would be to either copy all properties (like with Object.assign) or to use Object.setPrototypeOf on the ChildClass.

answered Sep 25, 2019 at 19:44

Bergi

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