Adding strings concatenates them:
> "1" + "1"
"11"
You have to parse them into numbers first:
/* parseFloat is used here.
* Because of it's not known that
* whether the number has fractional places.
*/
var a = parseFloat($('#a').val()),
b = parseFloat($('#b').val());
Also, you have to get the values from inside of the click handler:
$("submit").on("click", function() {
var a = parseInt($('#a').val(), 10),
b = parseInt($('#b').val(), 10);
});
Otherwise, you're using the values of the textboxes from when the page loads.