Multiple input validation test

HTML

<script src="http://ajax.aspnetcdn.com/ajax/jquery.validate/1.9/jquery.validate.min.js"></script>
<form id="testForm">
  <input type="number" name="a" value="1" data-relatedInput="b">
  <input type="number" name="b" value="1">
  <input type="submit">
</form>

JavaScript

$.validator.addMethod("sumLimit", function(value, input) {
  return +value + +$(input).closest("form").find("[name=" + $(input).attr("data-relatedInput") + "]").val() <= 10;
}, "Sum of values can't exceed 10.");

$('#testForm').validate({
  rules: {
    a: {
      sumLimit: true
    }
  }
});