Output all properties of object

I noticed that the auto-completion tab in IDE is able to output more fields than a call to eg.:
Object.getOwnPropertyNames(Bangle)
Object.getOwnPropertyNames(Bangle.__proto__)

Specifically, some object-like fields:
Bangle.on
Bangle.removeListener etc

Similarly for a Promise object, I do not see the .then function as child object. How can I get full listing via javascript?

The auto-complete is able to show all of these fields from a promise instance:

>p.
constructor         apply
bind                call
replaceWith         catch
then                clone
emit                hasOwnProperty
length              on
removeAllListeners  removeListener
toString            valueOf

How do I get these items into a javascript list?