Universal Properties and Methods

You can check which constructor created an object with o.constructor:
var d = new Date(); d.constructor==Date
There is a toString() method but its very uninformative:
var o={x:1,y:2};alert(o.toString());
The valueOf() converts to primitive type, for some objects like:
var now = new Date();alert(now.valueOf());
o.hasOwnProperty(s) returns true if o defines s and it is not inherited.
o.propertyIsEnumerable(s) like before but s would be enumerated by a for/in loop.
isPrototypeOf(), later..