Question

this is my 1st question in stackoverflow.

var str="Oct 13,2011";
var date1=new Date(str);
var date2=new Date(str);

of course
valueOf(date1)==valueOf(date2)

but why
date1!=date2

or say,how to determine 2 date object if they equal each other.

Date is a js object

Answer 1

Javascript objects are only equal if they refer to the same object-reference. Which is not the case in your code.

(reference: What is the standard definition of object equality for "=="?)

Edit: With a little type casting you can do:

var str="Oct 13,2011";
var date1 = new Date(str);
var date2 = new Date(str);

console.log(+date1 == +date2); // true