Annoying live validation with numeric prefixes

[Y-Less]

Prerequisites

• I have read the documentation;
• In the case of a bug report, I understand that providing a SSCCE example is tremendously useful to the maintainers.

Description

When live validation is enabled, typing in a negative number will flash up a warning for a moment when typing in negative numbers. I.e. after having typed only the - of -2, the live validation will complain that the input should be an integer, despite the fact that that is a valid integer prefix.

The same goes for typing . in front of a number. For a moment the warning flashes up then vanishes, which can be very annoying depending on the type of warning issued.

Steps to Reproduce

1. Add an integer field.
2. Press -.
3. Press another number.

Ideally, I'm providing a sample JSFiddle or a shared playground link demonstrating the issue.

Expected behavior

Ignore - and . when they are the only characters in an integer or number field, defer checking that they are the only character till form submission instead.

Actual behavior

Flashing warnings.

Version

You can usually get this information in your package.json or in the file URL if you're using the unpkg one.

[epicfaace]

Reproducible JSFiddle: https://jsfiddle.net/epicfaace/t329bLn0/

[epicfaace]

It's worth noting that this issue doesn't come up when ui:widget is set to updown.

[glasserc]

This is part of a larger constellation of issues about how we handle numbers. See #674. It's also kind of a problem with how live validation works -- it probably doesn't really make sense to validate until we get a blur.