var collListItem;
function QueryLastNewItem() {
    var clientContext = new SP.ClientContext();
    var List = clientContext.get_web().get_lists().getByTitle('Tracker');
    var query = new SP.CamlQuery();
    query.set_viewXml("<View><RowLimit>1</RowLimit><Query><OrderBy><FieldRef Name='ID' Ascending='False' /></OrderBy><Where><Eq><FieldRef Name='Status' /><Value Type='Choice'>New</Value></Eq></Where></Query></View>");
    collListItem = List.getItems(query);
    clientContext.load(collListItem);
    alert(collListItem);
    clientContext.executeQueryAsync(Function.createDelegate(this,
this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));
}

function onQuerySucceeded(sender, args) {
    //Once the list item is loaded, populate number field with the previous number field plus 1
    if ($("select[id^='Is_x0020_this_x0020_item_x002']").val() == "New")
        {
        $("input[id^='Number']").val(collListItem.get_item("Number")+1);
        }
}

function onQueryFailed(sender, args) {
    alert('Request failed. nError: ' + args.get_message() + 'nStackTrace: ' + args.get_stackTrace());
}