Prototypes and enumerable properties

[Christopher Benson-Manica]

I'd like to add a method foo() to all objects:

Object.prototype.foo=function() {
// whatever
}

The caveat, though, is that I do not want foo to be enumerable by a
for-in loop. Can I do that? If not, is there a way to derive a
subclass of Object for which foo is not enumerable?

 

[Douglas Crockford]

I'd like to add a method foo() to all objects:

Object.prototype.foo=function() {
// whatever
}

The caveat, though, is that I do not want foo to be enumerable by a
for-in loop. Can I do that? If not, is there a way to derive a
subclass of Object for which foo is not enumerable?

No. I think this was a design error in the language itself. The
JavaScript VM has a DONTENUM property, but it not available to the
programmer.

The best you can do is exclude functions while enumerating.

for (key in object) {
if (typeof object[key] != 'function') {
do your thing
}
}

http://www.crockford.com/javascript