How to properly extend JS native Classes

In many cases it can be useful to extend native Javascript classes. Though you should be careful as unwanted side-effects might be difficult to pin down. In this example we will be extending the Array class with a simple immutable remove function.

In order the extend a class we want to add a property to the object's prototype

We could simply do the following:

Here we directly extend the classes prototype. We however lack control to define detailed behavior. This causes unwanted side-effects. One of the side-effects is that the property is Enumerable. This causes it to be part of values when using a for...in loop. In order to circumvent this issue and get more control we can instead do the following:

By using Object.defineProperty we are able to control the attributes of our new property.