Why does subtracting from this variable inside an Interval go below and above 0?

Question

I can't figure it out and i feel like this is messing with my code in a larger scope. Shouldn't it just be dead 0? What am i missing?

var opacity = 1;
function FadeOut()
{

    fadeOutTimer = setInterval(() => {

        console.log(opacity);
        if (opacity <= 0)
        {
            opacity = 1;
            clearTimeout(fadeOutTimer);
            return;
        }

        opacity = (opacity <= 0) ? 0 : opacity - 0.1;
    }, 15);
}

<button onclick="FadeOut()" type="button">
Test
</button>