JAVASCRIPT

vanilla javascript fade out

<div id="target">Click to fade</div>
<script>
  function fadeOutEffect() {
    var fadeTarget = document.getElementById("target");
    var fadeEffect = setInterval(function () {
        if (!fadeTarget.style.opacity) {
            fadeTarget.style.opacity = 1;
        }
        if (fadeTarget.style.opacity > 0) {
            fadeTarget.style.opacity -= 0.1;
        } else {
            clearInterval(fadeEffect);
        }
    }, 200);
}

document.getElementById("target").addEventListener('click', fadeOutEffect)
</script>
<style>
  #target {
    height: 100px;
    background-color: red;
}
</style>

javascript fadein fadeout

#slideSource {
  opacity: 1;
  transition: opacity 1s; 
}

#slideSource.fade {
  opacity: 0;
}

vanilla js fade in fade out

event.target.style.transition = '0.8s';
event.target.style.opacity = 0;

javascript fadein fadeout

var slideSource = document.getElementById('slideSource');

document.getElementById('handle').onclick = function () {
  slideSource.classList.toggle('fade');
}

javascript fadein fadeout

<button id="handle">Fade</button> 
<div id="slideSource">Whatever you want here - images or text</div>
 Run code snippet