[RSS Feed/News] How to correctly read XF variable with Javascript

[XenForo]

I need to run a code according to the screen size.

So I've put the JS inside XF var and if I "alert" or "console.log" I can see the variable, but when calling the variable in XF it returns nothing.

How to correctly read the XF variable in this case?


Code:

<xf:set var="$screen"><xf:js>window.innerWidth;</xf:js></xf:set>
<xf:if is="{$screen} > 650">
     ...... code .......
</xf:if>

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