replace anything other than a-z,A-Z,0-9 or a space with nothing
<p>I am making a registration form. When a user is selecting a username I want jquery to replace anything other than <code>a-z,A-Z,0-9</code> or a space with nothing. </p>

<p>So on keyup the form field with the id of username will only allow <code>a-z,A-Z,0-9</code> or a space and replace anything else with nothing "".</p>

<p>How could I do that?</p>
