How to add a class to an object on click?

Question

css

Hello. I can't figure out why this is the code:

nextSlide = function () {
    var slide = document.getElementById("scalable");
    slide.classList.add("outDown");
};

Throws an error:

Uncaught TypeError: Cannot read property 'classList' of null

I would like to know why the error occurs...

Answer 1

there is no your "scalable" in jsfiddle.net/dk5g30jv/2 page

Answer 2

onclick="$(this).addClass('класс');"