Make selections from multiple drop-downs update when criteria is met

Question

I feel like this question is very vague, and I apologize because I can't seem to come up with a better name.

Ahem. As for the actual question. I've got two drop-down menus, and I'd like to make it so that whenever I have the correct value in each one, ex. Level 1 and Barbarian , it updates the connected fields. This works just fine with what I have here, but the problem is, if I leave Barbarian how it is and change the level to Level 2 , it won't update the connected fields until Barbarian has been switched to something else and then put back on Barbarian . How can I make it update right when the fields are the correct for a certain setup? I'm assuming some sort of listener, but I really don't know all that much about Javascript, as I'm new to it all.

function classDefine(){
var playerClass = document.getElementById('class').value;
var playerLevel = document.getElementById('level').value;
if (playerClass == "Barbarian" && playerLevel == "Level 1") {
document.getElementById("fort").value = 2;
document.getElementById("ref").value = 2;
document.getElementById("will").value = 2;
document.getElementById("baseAttackBonus").value = 2;
}
else if (playerClass == "Barbarian" && playerLevel == "Level 2"){
document.getElementById("fort").value = 5;
document.getElementById("ref").value = 5;
document.getElementById("will").value = 5;
document.getElementById("baseAttackBonus").value = 5;
}
}

Answer 1

You can use the onChange listener on each of the select boxes to run the function whenever either of them changes.

<select id="class" onChange="classDefine()">
    <option>...</option>
</select>

or in javascript

document.getElementById('class').addEventListener("change", classDefine);

Answer 2

You can use the change event handler that gets activated whenever a new selection is made in your dropdown. You can add one for each of your dropdown and then put your logic for addressing the corresponding matches between the two. Below is an example of how you would attach an event handler to one of them.

document.getElementById('class').addEventListener("change", function (event) {
     //your logic
     alert("something new was selected"); 
});

How this helps.