re-use regular expression on clientside for onkeyup event

For my xpages/jsf application I have setup for an xe:input control the following validation:

<xp:this.validators>
<xp:validateConstraint
    regex="${application.regex_email}"
    message="please follow the rules">
</xp:validateConstraint>
<xp:validateRequired
    message="follow the rules">
</xp:validateRequired>

</xp:this.validators>

The regular expression I use:

regex_email=^([w-]+(?:.[w-]+)*)@(acme.org|acme.com)

(so I allow only email addresses from acme.org and asme.com domains).

This works fine but I want to apply the same to validation to the client-side, so in the onkeyup event that same (or similar) regex is used. But I do not know how. Can anyone explain how to?

Basically I want to prevent that users enter capitals in the allowed mail domains.