Manually Abort JavaScript?

I'm playing around with forms and wrote a JavaScript
function that loops through all form elements and displays every option
in every select field with an alert for each one.

var els = form.elements;
var l = els.length;
for (var i=0; i<l; i++) // loop through all form elements
{
if (els[i].type.substring(0,6) == 'select')
{
var options = els[i].options;
for (var j=0, len=options.length; j<len; j++)
{
alert(els[i].name + ' option ' + j + ' = "' + options[j].text + '"')
}}}

In the form I am using this results in many alert boxes popping up.

This seems like a very, very basic question, but I've Googled it quite a
bit and can not find an answer. Is there a way to manually abort that
script (other than closing my browser) or do I have to keep clicking OK
until the loop has run it's complete course?