How to get Element of Webpage

I was wondering how to only get an element of a webpage which I am parsing the data in.

Currently I am getting the whole webpage like this:

var con = Titanium.Network.createHTTPClient();
    con.open('GET', 'http://www.example.com/');
    con.onload = function()
    {
        Ti.API.info(this.responseText);
        $.label.text= this.responseText;
    };    
    con.send();

I am thinking that just getting part of the webpage would be quicker but if there is no performance difference using alternative methods as they still get the whole webpage but only return part then let me know.