javascript: the field value of the loaded list item unexpectedly returns "NaN"

I am trying to query the last item in the current list where status = New, so I can automatically fill in one of the fields based on the value of the previous item. Executing "alert (collListItem);" it shows "(object) (Object)", and the onQuerySucceeded function is actually being activated, however, the value you enter is "NaN" when it should be the value of the field of the previous number +1 (the previous value is 1) .

var collListItem;
function QueryLastNewItem() {
    var clientContext = new SP.ClientContext();
    var List = clientContext.get_web().get_lists().getByTitle('Tracker');
    var query = new SP.CamlQuery();
    collListItem = List.getItems(query);
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") 

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

Since the query seems to be successful, I am confused as to why the value is not assigned properly. I thought it could be because "collListItem" could be considered a collection of objects, but I have set the row limit to 1 in the CAML query, so it should only contain 1 element.

Any help or suggestion is greatly appreciated.