I don’t think that is possible as JS doesn’t know to do something in that tag.
you could try phx-value-newParam="javascript:doSomethingInJs('<%= floor.number %>');"
but I highly doubt browser will execute that.
You can try setting the calculation from a function via dom yourself?
document.getElementById('specialButton').attr('phx-value-newParam', doSomething('<%= value %>'))
ps: that is a pseudo-code…
maybe look into even listeners and hooks? seems like that is gonna be useful in your case rather than the hacky code I just proposed
https://hexdocs.pm/phoenix_live_view/js-interop.html#loading-state-and-errors
