traler,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
</head>
<body>
<form action="http://" name="form">
<input name="input" value="3.14">
</form>
<script>
alert(parseFloat(document.form.input.value) );
</script>
</body>
</html>