govuk-prototype-kit
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alphagov
It's hard to do form validation in the Prototype Kit
This come up on support so just recording the issues around validation in one place.
To validate a form you would check the data in a route. If it's not valid you could redirect back to the original page with, for example ?error=age. You can use that data on the page to show an error summary and error message.
However the auto data store feature means error=age is now stored in session - if a user comes back to this page the error will still show even if they fix it.
Some fixes:
You could remove the data from session manually if the validation checks pass:
delete req.session.data.error
You could use render instead of redirect in your route, which avoids passing the error data from page to page, but rendering on POST means the user sees a nasty warning if they refresh the page or press back to return to it.
You could use the _ naming feature to avoid auto data store(_error=age), but it also means data is not sent to the page, so you'd have to write a route to send it to the page:
res.locals.error = req.query._error
It would be good to have a standardised approach so people don't have to work it out for themselves, and don't use different approaches.
Related
- #978
- #509
