Question

Is it possible to strip everything from a text box, except that which is defined by a regular expression, on each keyUp event?

For example, I have a text box and the regex ^[a-zA-Z0-9]+$. Whenever the user enters (or pastes) characters, it will strip any characters that are not contained in that regular expression.

Answer 1

You could use a regexp replace with a negated character class (I also abbreviated the character, made it case insensitive, and did a global replace)

var input = document.getElementById('sandbox');    
input.onkeyup = function(){
  input.value = input.value.replace(/[^a-z0-9]/ig,'');
}

In action: http://jsfiddle.net/theprawn/GvbKY/