Check field value of front end form prior to sending to database

Hi all,

I am building a front end form and I would like to be able to check a field value and perform some editing of the returned value upon pressing submit button BUT prior to sending to the database.

I know of the get_field_object but it does not seem to work for me. I suspect that this retrieves data from the database(??)

Is there anyone with experience on the issue? I understand that basically what I want to do is what a javascript would do but my knowledge on JS is null…

Thanks a lot,
Harry

https://www.ads-software.com/plugins/advanced-custom-fields/