I am validating a field which may NOT be anything but numbers, but may include a space or a minus-sign.

This is for validating phone number field!
So, these criterias should be met: (might have forgot a criteria, if so remind me)

```
 1- Atleast 5 numbers
 2- May contain space
 3- Not shorter than 5 characters
 4- Not longer than 20 characters
 5- May contain minus-sign
 6- Not empty

 if (nr.length>4 && nr.length<21 && nr!=''){

 }

```

How should I write the regexp?
Or the if statement?

Thanks