My goal is, that eForm populates hidden fields with data my script receives from a database. I was able to successfully populate all visible input fields with my function called through &eFormOnBeforeFormParse. When I want to populate hidden fields, it does not work. They are empty or MODx/eForm complains that the form was tampered with.
I could just throw the data in regular input fields and hide them with css, but is there a way to do this appropriately with type="hidden" fields?
Use the eform attribute to prevent validation of hidden fields:
<input type="hidden" name="calculatedField" value="" eform="::0::" />
More info here: http://wiki.modxcms.com/index.php/EForm#Hidden_fields.2C_select_boxes.2C_radio_options_and_checkbox_fields