correct array reference syntax

I am using a js calendar script that populates a text field with a date. When clicking in the field the calendar shows then i choose a date, calendar closes, the date is now in the field. great it works fine.

example- *note, array use[]*

<input type="text" id="example[]" name="example[]" value="" onfocus="if(self.gfPop)gfPop.fPopCalendar(this);return false;">

Code (markup):

I want to make this call from a button. when adding the code to a href, the popup shows but nothing happens when selecting a date. I have tried the following scripts will failure.

*html a href and img tag left out*

onclick="if(self.gfPop)gfPop.fPopCalendar(document.this_form.elements['example[]']);return false;"

onclick="if(self.gfPop)gfPop.fPopCalendar(document.this_form.example[]);return false;"

onclick="if(self.gfPop)gfPop.fPopCalendar(this);return false;"

Code (markup):