Is it possible to restrict an edittext to only numbers?

Why not use a Slider Expression as the userInput area?

Yes it is possible with an onChange function and a regular expression (regEx).

For example, the following function will only allow digits [0-9] and remove any other character (after you press enter):

myEditText.onChange = function() {
     this.text = this.text.replace(/[^\d]/g,'');
} // end function

The regEx value /[^\d]/g is explained like so:

/[^\d] = Match a single character not present in the list below

\d = matches a digit (equal to [0-9])

/g = All matches (don't return after first match)

So, the whole function looks for all characters -in the given EditText field- except digits from 0 to 9 and replaces them with nothing (the double single quotes '').

(This however does not include negative numbers, because it will also remove the minus character.)

You can test and learn about regular expressions (regEx) at several on-line sites like https://regex101.com

Hope this helps.