Hashmap elements in a request form

[Susan]

I have an http request form containing a hashmap as a request
parameter. Is it possible to retrieve a value from one of the hashmap
elements using JavaScript?

For example:
onclick="alert(document.myform.myMap['mapFieldKey'].value)"

This should show an alert box containing the value of an element in the
hashmap. Is this possible? I have yet to figure out a syntax that will
accomplish this. Any suggestions?

Thanks.