Question

This works, with a simple button calling the addDamage function:

var damage=0;
function addDamage()
{
damage+=10;
document.getElementById("p1s").innerHTML=damage;
}

This doesn’t:

var damage=0;
function addDamage(who)
{
who+=10;
document.getElementById("p1s").innerHTML=who;
}

With this button:

<button type="button" onclick="addDamage(damage)">Add</button>

It’s probably obvious. I’m really new. Thanks!

Answer 1

Cheeso has identified the basic problem, which is that JavaScript parameters are passed by value. To get the behavior you want, you can wrap your counter in an object:

var player1 = { damage: 0 }; 

function addDamage(who) {
   who.damage+=10;
   document.getElementById("p1s").innerHTML=who.damage;
}

Then your button would do this:

<button type="button" onclick="addDamage(player1)">Add</button>

Presumably you would have other properties for player1 that you could put in the object as well.

To make the addDamage more flexible, you could also pass a second parameter to tell where you want to display the results:

function addDamage(who, outputId) {
   who.damage+=10;
   document.getElementById(outputId).innerHTML=who.damage;
}

Then button looks like:

<button type="button" onclick="addDamage(player1, 'p1s')">Add</button>