Question

I want to be able to test if theForm is defined, meaning it found a form with the name ‘data’
How do we do that?

Then if it is not found I can test for the other form name and set the action on that named form.

function edit_OnClick() {
    var theForm = window.document.forms['data'];

    theForm.action = "checkout.asp";
    theForm.submit();

    return false;
}

Is it ok to post follow ups at stackoverflow?

This is what I came up with using your advice, but it is not switching like I planned.

    function edit_OnClick() {
        var theForm = window.document.forms['data'];
        if ( typeof ( theForm !== "undefined" )) {
            theForm.action = "checkout.asp";
            theForm.submit();

            return false;
        }else {
        var theForm = window.document.forms['form_bml'];
            theForm.action = "checkout.asp";
            theForm.submit();

            return false;
        }
    }

Answer 1

You could use:

var theForm = document.forms['data'];

if (theForm) {
  // do stuff
} else {
  theForm = document.forms['form_bml'];
  if (theForm) {
    // do other stuff
  }
}

If the actions for both are the same, then:

var theForm = document.forms['data'] || document.forms['form_bml'];
if (theForm) {
  // do stuff
}