Phone It In
A phone number entry helper
Many other phone number data entry helpers act as in-place templates, enforcing format with every character typed and automatically filling in parentheses and dashes. It is very hard to implement this reliably, and at the same time, it can break users' expectations of what they should be able to do with an input on a form, such as paste in a value.
This helper takes a different approach and opens a helper next to the input that dynamically shows what the formatted phone number will look like, whether there are any problems, and whether entry is complete. Upon leaving the input, the value is re-formatted to standard.
Note that this code currently relies on features only present in up-to-date modern browsers.