function bar(){
 return this.html();
}

alert($('#foo').bar());

jQuery.fn.extend({
    bar: function() {
        return this.html();
    }
});

alert($('#foo').bar());

function bar() {
    return this.html();
}

bar.apply($('#foo'));

obj = {x: 1};
obj.prototype.bar = function() {return this.x;};
obj.bar();

("#foo")[0].getHtml = function () {
  return this.innerHTML;
};
alert($("#foo")[0].getHtml());