Is there way to override jQuery's core functions ? Say I wanted to add an alert(this.length) in size: function() Instead of adding it in the source

size: function() {
    alert(this.length)
    return this.length;
},

I was wondering if it would be possible to do something like this :

if (console)
{
    console.log("Size of div = " + $("div").size());
    var oSize = jQuery.fn.size;
    jQuery.fn.size = function()
    {
        alert(this.length);

        // Now go back to jQuery's original size()
        return oSize(this);        
    }
    console.log("Size of div = " + $("div").size());
}