Why does replace javascript work crookedly?

Question

JavaScript

Somehow replace works strangely, I need to prohibit the input of certain characters, and if it works at the beginning of the line, then it stops
Code: https://jsfiddle.net/sL5mqudn/1/

Answer 1

You are only replacing the first character. You could add the /g modifier and remove the characters from the beginning and end of the line
/[а-я, 0-9]/g
But in general, it is better to do such things through preventDefault()

Answer 2

You have written in: replace a string consisting of strictly one set character (capital Cyrillic letters, numbers, comma or space) with an empty string.
What is wrong with your program?