How to get combo box after initializing it

I have a combo box already initialized on a page from HTML.

I want to access that combo box but from a different JS file that the box was not initialized from. How can I get the instance of the combo box?

initializing a combo you assign a name to it:

var myCombo = dhtmlXComboFromSelect("combo_zone1");

so you can access this combo by this name myCombo

Thanks, I didn’t give it a name attribute.