opacity animator in J (minifiled)

index.html

<script src="https://gist.github.com/awesomelewis2007/4ac3ea55bfae27f68adfadf6c6d1969d" async defer></script>

opacity.min.js

function sleep(t){return new Promise(e=>setTimeout(e,t))}async function opacity_to_100(t){var e=0;for(let o=0;o<25;o++)document.getElementById(t).style.opacity=e+"%",e+=4,await sleep(10)}async function opacity_to_0(t){var e=100;for(let o=0;o<25;o++)document.getElementById(t).style.opacity=e+"%",e-=4,await sleep(10)}