Object.getOwnPropertyNames() returns an array containing all the names of the own properties of the object passed as argument, including non-enumerable properties. It does not consider inherited properties.

Non enumerable properties are not iterated upon. Not listed in for..of loops, for example.

To get only a list of the enumerable properties you can use Object.keys() instead.

Example:

const dog = {}
dog.breed = 'Siberian Husky'
dog.name = 'Roger'

Object.getOwnPropertyNames(dog) //[ 'breed', 'name' ]