<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Documento sin título</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
</head>
<script>
function sumar()
{
var num1 = parseInt(document.forms["form1"]["num1"].value);
var num2 = parseInt(document.forms["form1"]["num2"].value);
var suma = num1 + num2;
document.forms["form1"]["suma"].value = suma;
}
</script>
<body>
<form name="form1" method="post" >
<p>
<input type="text" name="num1">
</p>
<p>
<input type="text" name="num2">
</p>
<p>
<input type="text" name="suma">
<input name="Sumar" type="button" onClick="sumar()"id="Sumar" value="Enviar">
</p>
</form>
</body>
</html>