<button onmouseenter="enter(event)" onmouseleave="leave(event)">state</button>
<script>
function enter(event) {
event.target.style.background = "blue";
setTimeout(function () { event.target.dispatchEvent(new Event("mouseleave")) }, 2500)
}
function leave(event) {
event.target.style.background = "";
}
</script>