Tip Calculator Using HTML/CSS, SCSS, GULP and JavaScript OOP

I want to prevent input fields to accept zero as first character, here's what I have tried. I used addEventListener with keydown event to detect type of character, then store the key (e.key) in an array container and access that character using array index number. If the character is zero, then it will return a returnValue of false (e.returnValue = false) to prevent zero from being typed in the input field. This works but if user made a mistake and deletes characters using backspace, then the input field will now be able to accept zero as first character again.