It took me too long to figure out how to put my extensive JavaScript code into the ISV.config xml. Eventually it worked, but a far more easier way is to trigger the JavaScript, is to put a function name in the xml file and put the contents of the function in the onLoad of your form. As I reminder to myself, I stored it over here.
(In case the ISV button is not placed on the a form, but for example on a view, than you still have to put the JavaScript into the xml file.)
Here is a xml example of the ISV.config part:

And the onLoad script example:

Function_onclick = function()
{
alert('Button has been clicked');
}