Question

In nodejs documentation for the util.inspect function, the documentation states that “If showHidden is true, then the object’s non-enumerable properties will be shown too.”

Does non-enumerable properties refer to prototypes only? Or are there other non-enumerable properties I haven’t considered?

Link to documentation in question: http://nodejs.org/docs/v0.4.8/api/util.html#util.inspect

Answer 1

Enumerable properties and prototype properties are unrelated. It just happens that most (all?) of the prototype properties on native objects are non-enumerable.

To show that both prototype and instance properties can be both enumerable or non-enumerable:

You can create non-enumerable properties on your own objects with defineProperty():

var obj = {};
Object.defineProperty(obj, 'a', {
    value: 1,
    enumerable: false
});

On the other hand, prototype properties that you add (non-native) are by default enumerable, even if you add them to the prototypes of native objects:

Object.prototype.a = 1;
var obj = {};

// Will log "a"
for (var i in obj) {
    console.log(i);
}