Is it possible to define the get item of a javascript object as a function?

Question

I want to define some class or object where I can do

Foo['bar']

This get item call should call a function so that I can provide a default or some other logic based on the key. Similar to python's __getitem__

const Foo = {
   __getitem__: key => {
     if (key in Foo.values) return Foo.values[key]
     // other logic
     return key
   }

}