There are many things wrong with your code. Let me explain where and what:
xhttp.open("GET", "books.xml", true);
document.getElementsByIdis wrong, since there is only one id, it should be:
jQuerythe syntax would be
$('#forPrice')but since you use native JS, you must omit
document.getElementById('forPrice')-> note the lack of
.innerHTML = 'text')
catalogto specific values (you can revert this change if you feel like it).
)that are not allowed.
All in all, what I changed is not totally correct, but at least the data gets loaded. However, since you do not check what has been selected from the select-option element, the data gets overwritten.
Hope this helps you get going on the right direction!
Here's the link to the working example. http://plnkr.co/edit/4TrjfX4LI8234lFVwIyU?p=info