问题:

I am not sure if it is possible but I would like to leave the HTML <select> object expended using JavaScript, JQuery after the selection. Any ideas?

EDIT

What I want is that; if user selects more option from select list, I will append some more options to select element and leave it open. If user selects something other than more option, I will collapse the list. I can get a hold of other functionality but only problem here is to keep the select element open.

回答1:

It's not possible directly. You'd have to implement something that looked and worked like a native <select> but which also had the feature you want.

edit — check Mr. Kling's answer; there might be a way to make that work, sort-of.

回答2:

You could come very close with this:

$('#selectID').change(function(){
    $(this).attr('size', $(this).children().length);
});

The size attribute specifies how many options to display (default is 0).

DEMO

You might have to make some tests whether this works in every (recent) browser. But imo this would be better than trying to simulate a select box (screen readers, etc).