But then it turns out that you really do want a free-form text input. Let people paste text in, edit their text freely, then let it validate afterwards. When it validates, then reformat it.
For example, text boxes with length limits. These are awful. It messes with your ability to paste something in, then edit it down to the correct length.
You can validate roughly anywhere, but at the absolute earliest, only re-format on blur. Never earlier. You have no idea what the user might be doing in the meantime.
And even then, I'd strongly suggest not changing what they entered. Change it to a display-only element with nice formatting if you want, but don't screw with their input.
- pasting from Word
- QA testers being through
- devs pranking each other
The third one is by far the most common. Word is much better these days and I've not seen that happen in a long time. I wish I saw QA test this stuff more often. The idea that it's common enough that you'd break your UX to handle it baffling to me.
For example phone numbers can be a string of digits, or multiple strings separated by spaces or hyphens or with parts enclosed by () etc
It's a more pleasant UX to let them paste anything, then edit it inside the input, validate and submit.
What I have found to work well is when the user unfocuses the input field or on submit strip everything but expected values then validate. If you want you can format the value at this time too (and the formatting won't interfere with text input).
If you want to get really fancy you can strip and format as they type and be careful to keep the formatting "virtual" such that the user is only editing the raw digits but this is very tricky to get right on all platforms and support all expected native editing UX. But even in the best cases this can have bad edge cases. For example the user pastes some text but it happens to have multiple numbers in it, if you eagerly strip and format what is left for the user will be these two numbers mushed together with misplaced separators or similar. If you let them paste, remove the unintended stuff, then format on blur this just works and is understandable.
You could remove the zero-width spaces in validation (for eg a phone number).
If I ever grew to hate users this much, I would find a new career. You should consider that.
Which is really nice for copy pasting. For example, I have a number with spaces in it, and when I paste I get nothing or only until the first space because someone decided I'm not allowed to have non-numericals in the input field at anytime.
And final validation needs to happen on the server side anyway - anything before that is just a usability helper.
