For actionparam

[quintenjiang]

I follow the sample:
<a4j:actionparam name="w" value="screen.width"
assignTo="#{userBean.screenWidth}" noEscape="true" />

to pass width of scrren to bean. When I try to pass the width of the content area of the browser window. like

<a4j:actionparam name="w" value="window.innerWidth"
assignTo="#{userBean.screenWidth}" noEscape="true" />

I does not work; what is wrong?

Thanks