[Input] How can I get the value if the input value is not a valid number for type="Number" Input?

[Xidai]

Consider this scenario, there is a Input with type="Number", I only type '-' into the Input and focus out, the '-' is not a valid number, so the event.target.value returns empty, but what we need is to highlight it with error state to tell the user this is not a valid number so that he/she should modify it. But I can not get the real input '-'. Is there any way I can achieve that?