<html>
<title>JS introduction</title>
<head>
<script>
function calculate(n)
{
var a=parseInt(document.getElementById("t1").value);
var b=parseInt(document.getElementById("t2").value);
var c=0;
if(n=='+')
c=a+b;
else
c=a-b;
document.getElementById("t3").value=c;
}
</script>
</body>
<form>
<center>
number1<input type="text" id="t1"><br>
number2<input type="text" id="t2"><br>
result<input type="text" id="t3"><br>
<input type="button" value="Sum" onClick="calculate('+')">
<input type="button" value="Diff" onClick="calculate('-')">
</center></form>
</body>
</html>