JSFiddle - React, Tailwind, and code Playground

HTML

<div class="block"></div>

CSS

.block {
    position: relative;
    width: 100px;
    height: 100px;
    background: tomato;
}

JavaScript

var block = document.querySelector('.block');
var player = block.animate([
    {
        left: "0"
    },
    {
        left: "100px"
    }
], {
    duration: 1000,
    delay:    1000,
    endDelay: 1000
});

//アニメーション終了後endDelayで指定した1000ms後に発火
player.addEventListener('finish', function(){
    alert('done!');
}, false);