 <p>The URL you're passing in the example above is:</p> <pre><code>'DCC?command=' + encodeURIComponent(command) </code></pre> <p>The <code>DCC</code> part is actually part of the path to the webpage. It's short because it's a relative path. The fully qualified path would look something like www.sitename.com/DCC<br> The part after that (after the <code>?</code> character) is called the query string. That's the part of the URL that contains data that you're passing to the server (in a GET transaction), and it follows this pattern:</p> <pre><code>a=somevalue&amp;b=anothervalue&amp;c=yetanother </code></pre> <p>So add "&amp;varnameA=valueA" to that string to pass both <code>command</code> and <code>varnameA</code>:</p> <pre><code>xhr.open('GET', 'DCC?command=' + encodeURIComponent(command)+"&amp;varnameA=valueA",true); </code></pre> <p>You can keep tacking on &amp;varname=value strings until your query is around 2000 characters, because that's where browsers commonly start crapping out because the URL is too long.<br> Remember to encode any special characters in the values (that's what <code>encodeURIComponent()</code> is being used for) or you'll get some weird behavior. That means that you're appending something like <code>+"&amp;varnameA="+encodeURIComponent("valueA")</code> for each additional variable/value pair you want to pass to the server.<br></p>