[devote]

<textarea id="area">&lt;test&gt;<</textarea>
<script type="text/javascript">
    var area = document.getElementById( 'area' );

    alert( area.innerHTML );

    // либо так:
    var html = area.value.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;").replace(/"/g, "&quot;");

    alert( html );
</script>