How to send a variable to a function?

Question

JavaScript

How to send a variable to a function?

function putDayBall(l) {
        alert(l);
}
<label onclick="putDayBall('D')">D</label>

If I write function putDayBall(var l) - then idea writes that there is an error

Answer 1

What is the problem?
https://jsfiddle.net/qfjatfut/