Watch all properties on objects, including properties created later

Say I have an object, var obj = {}. I want to have a handler invoked when at a later time, any field is retrieved; obj.b.

I am aware of proxies,

var obj = {};
var proxy = new Proxy(obj, {
  get(obj, prop) {
    console.log('get', prop)
    return Reflect.get(obj, prop);
  }
})

However, this will only log when accessing properties through the proxy proxy.b and will fail to log otherwise obj.b.

I am also aware of using defineProperty to put getters on all the keys of obj. However, this won't handle new fields that are added to obj after the getters were added.

Maybe if it's possible to re-implement proxy, then it should be possible to add the handlers to the original obj instead of the proxy. I've tried investigating the proxy object, but it seems to be implemented internally. new Proxy({},{}) has properties [[Handler]], [[Target]], and [[IsRevoked]], but I was not able to access or view these objects; proxy['[[Handler]]'] returns undefined. I was thinking if I could just add those handler and target fields to obj myself, instead of creating a separate proxy object, then I could make obj act like a proxy.

I have read through MDN's docs for proxies, defineProperty, and handlers and even http://exploringjs.com/es6/ch_proxies.html. I've likewise come across multiple stack overflow posts achieving something similar but not quite complete.