<script LANGUAGE="JavaScript">
function compute(form)
{ form.result.value = eval(form.expr.value) }
</script>
<form>
Eingabe: <input TYPE="text" NAME="expr" SIZE=15>
<input TYPE="button" VALUE="Berechnen" ONCLICK="compute(this.form)">
<br>
Ergebnis: <input TYPE="text" NAME="result" SIZE=15>
</form>