Turist,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script>
window.addEventListener('DOMContentLoaded', function() {
var select = document.querySelector('select');
select.addEventListener('change', function() {
var val = [{a : 1, b : 2},{a : 3, b : 4},{a : 5, b : 6},{a : 7, b : 8}][select.value];
var num1 = val.a, num2 = val.b;
alert([num1,num2])
});
});
</script>
</head>
<body>
<select name="" size="1">
<option value="0">a</option>
<option value="1">b</option>
<option value="2">c</option>
<option value="3">d</option>
</select>
</body>
</html>