Allow only certain characters

Question

I'd like to block all characters from being inputed except 0-9,a-z,A-Z range only alphanumeric characters. So when someone types ! for examplee nothing is written into input. How can I do that?

Answer 1

You need to write a function that listens for the onkeypress event for the form field, then check to see if the form contains any unwanted characters, and if it does, you update the field with those characters removed.