id.js

var id = (function() {
	var uid = 0;
	var dic = Object.create(null);
	var map = WeakMap();

	return function id(obj) {
		if (!(obj instanceof Object))
			return obj in dic ? dic[obj] : dic[obj] = uid++;

		if (map.has(obj))
			return map.get(obj);

		map.set(obj, uid);
		return uid++;
	};
})();