By doing some experiments with this ,I came upon the following:
var foo={foo:'bar',hello:'world'};
$.fn.test=function(){return this;}
$(foo).test()===$(foo); //returns false
I cannot explain why the last comparison returns false. I am sure that this when calling function $(foo).test is $(foo)...
The same thing happens with $(this).test()===$(this) which returns also false; however $(this).test()[0]===window returns true as expected.
Any explanation?
When you do $(foo), you are executing a function that creates a new jQuery object.
If you try your example again but by storing the object in a variable it should work as you expect:
var $foo = $(foo);
$foo.test()===$foo; //=> true
This is because comparison between objects in JavaScript is done by identity, not by their content.
If you know a language like C you should understand why, if not I'll try to explain:
var x = { a: 1 };
// What happens in memory is that the variable x stores a pointer to a location
// in memory with the actual content. So in C, if you tried to print x, you
// would get a long number instead of the actual object, eg: 2435080915
var y = { a: 1 };
// Now we created another object with the same content, but the content is
// duplicated in memory, it's not at the same place than x, because if it was,
// a modification to y would also affect x. So the pointer is
// another number, eg: 7043815509
// So when we do:
x == y
// what happens is that JavaScript compares the two numbers:
// 2435080915 == 7043815509
// which returns false.
