I am trying to add Javascript to a Marketo LP using a Marketo form that adds a date/time stamp to the submission. I have created a new field in Marketo named Last Form Submission Date (lastFormSubmissionDate) and am adding the field to the form. Then on the Marketo page I am adding this code to the Custom Head: <script> MktoForms2.whenReady(function(mktoForm){ mktoForm.onSubmit(function(mktoForm){ mktoForm.addHiddenFields({ lastFormSubmissionDate : new Date().toISOString() }); }); }); </script> It is not populating the field though, so wondering what I am doing wrong.

The specific reason your code doesn’t work is it has a dependency on the global MktoForms2 object and you’re loading it in the <head>, while the Forms 2.0 library loads somewhere in the body. Move the code just before the closing </body> tag and it’ll work. As for doing this on the form vs. in a Smart Campaign, I like doing it on the form because it will really capture the form submission time.