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Yep, this is known as input masking, and I wish browsers would just natively support this through various input types, because it's been the bane of my existence.

Phone inputs are especially painful to mask since you have to deal with a mind-boggling number of format variations.

The (new-ish) ‘Intl.NumberFormat’ API solves this issue

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

No, it doesn't. You can't apply that to a number input.

It can, you just have to mask the input somehow (which can be very involved). In particular you would use numberFormat.formatToParts() and then add the parts to as the mask element interacting differently based on the type.

I would not provide the user the ability to type a separator, but rather keep their number formatted with them in the appropriate places.