Difference between $(this) and this in jquery

What is the fundamental difference between using $(this) vs this

$('.viewComments').click(function(ev){
    //returns the desired value
    alert(this.getAttribute('id'));

    //Gives an error sayin function is not defined 
    alert($(this).getAttribute('id'));

    //returns the desired value
    alert($(this).attr('id'));
});

What I thought was "$(this)" will contain all functions that "this" has and more..But that doesn't seem to be the case.

So what exactly is $(this)? and

Hw do I know what functions are available when I'm using it? (I know I can get them through firebug. but I would like to know if there any some other way- some doc may be)

Solution 1:

this is the DOM object, whereas $(this) is the jQuery wrapper around same.

When using this, you can call DOM methods on it, but not jQuery methods. When using $(this), you can call jQuery methods on it, but not DOM methods.

Solution 2:

$(this) - represent current DOM element on which event this function is called

The this keyword - In JavaScript this always refers to the “owner” of the function we're executing, or rather, to the object that a function is a method of.