Override a class

[Wicken_Hey]

I want to rewrite a class to overwrite the original class. For example, I want to override the Primitive class.
Before version 1.95, I can write this:

function Primitive(){
 }
Cesium.Primitive = Primitive;

But now in the 100 version, it is no longer possible.
It reports the following error：

What should I do now?

Thank you.