The GWT editor runs validations on translations as they are typed, and immediately displays problems detected by the validators.
The React editor should be able to run any of the standard validators, based on the settings for the project-version (off/warning/error).
List of validators (taken from GWT editor validation options):
Leading/trailing newline (\n)
Positional printf (XSI extension)
Tab characters (\t)
XML entity reference
Integrate Validators with alpha editor Validation component
Apply Validators selected as Warning / Error in validation option settings
We have a few options here:
Provide a REST service (on the server) which runs the existing (Java) validations. Note that the cost of sending the text to be validated could be significant, especially for large strings. On the other hand, this might allow us to create new validations which require server-side resources, eg "msgfmt -c".
Long term, it might also make sense to combine some of the options, eg provide a REST service for special server-side validations, but have other validations which can be run on either browser or server (using either Nashorn or GWT).
In the short term, I think a REST service for validation is our best option for getting a working solution in a reasonable time, while still allowing the validation code to be shared between React and GWT during the transition.
covers the implementation of the frontend