One notable difference is that `foo.method` is bound to `foo` in python, but unbound in JavaScript. This leads to lots of `foo.method.bind(foo)` because the former didn't DWIM.
One case that comes to mind is how each language implements (what I call) the continuation pattern. Suppose you want to iterate over the vertices of a binary tree. In JavaScript, you would accept a callback parameter which you call with each vertex. In Python, you would yield each vertex to the caller. These are very different styles and lead you in different directions.
The key similarities in my mind are:
1) In both python and javascript, the class and prototype are exposed and can be called explicitly if desired:
MyClass.method(my_instance, arg1, arg2)
MyClass.prototype.method.call(my_instance, arg1, arg2);
bound_method = my_instance.method
bound_method = my_instance.method.bind(my_instance);
Can anyone think of any other common ground?