e.g. in https://github.com/angular/zone.js/blob/master/lib/utils.js#L91 properties such as _fn, _addEventListener are attached to foreign objects which risks interactions with any other libraries that may also be using these properties.

I think we could use Symbols if the environment supports them, with strings as a fallback, to attach/read these properties.

@vicb