Why does this function work (closures in javascript)?

Question

JavaScript

There is a code:

The code

var div = document.querySelector('.test');

    function hide(elem, t) {
        var fadeEffect = setInterval(function () {
            if (!elem.style.opacity) {
                elem.style.opacity = 1;
            }

            if (elem.style.opacity < 0.02) {
                clearInterval(fadeEffect);
                elem.style.display = "none";
            }

            elem.style.opacity -= 0.02;
        }, t)
    }

    div.onclick = function () {
        hide(this, 19);
    }

Link to jsfiddle.
Gives a fadeOut effect like in jQuery. I tried stuffing the inside of the setInterval into a function. And to my surprise, I succeeded. But I don't understand why I can still insert my argument tinto the arguments of the function hide(). Thank God of course that works, but I would like to figure it out!
I just thought that I twould not be able to reach the time argument in setInterval.

Answer 1

I don't understand anything. You pass the t parameter to hide. Inside hide, you use the t parameter as an argument to the setInterval function.
Because you declared that the function can have a parameter t and passed it.