<html>
<body>
<div>
<div id="float1" style="border: 2px solid red; height:100px">I should become a right-floating element.</div>
This text should be on the left.  The float should be to the right.
</div>
</div>

<div style="height:30px"></div>

<div>
<span id="float2" style="border:2px solid red; height:100px">I should become a left-floating element.</span>
This text should be on the right.  The float should be to the left.
</div>

<script>
document.getElementById("float1").style.cssFloat = 'right';
document.getElementById("float2").style.cssFloat = 'left';
</script>