How to add class name to all elements starting with a specific id?

Before you criticize me, I know this question may be a duplicate. I have tried every other post I found on stackoverflow but failed.

I want to add a class name to all elements in my html that start with 'subclass', then a number (classid), then a random number. I don't exactly know how many elements there are since it's dynamically generated via a servlet.

Here is the code I am trying to run:

<style>
.bold {
    font-weight: bold;
}
</style>
<script>
function highlight(classid){
    alert(classid);
    $("p[id^='subclass'+classid]").addClass('bold');
    alert('hello world');
}
</script>
<p id='subclass25'>Hello World </p>

I get an alert for classid but not for "hello world". So I'm pretty sure my JQuery is wrong....