<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<button id="idBtn">open</button>
<div id="idDiv" style="width: 200px;height: 200px;background: #00f" hidden="true">ТУТА мИнЮ</div>
<script>
let div=document.getElementById('idDiv');
let btn=document.getElementById('idBtn');
btn.onmousedown=()=>do1();
function do1() {
div.hidden=false;
btn.innerText='Close'
btn.onmousedown=()=>do2();
}
function do2() {
btn.onmousedown=()=>do1();
btn.innerText='Open';
div.hidden=true
}
</script>
</body>
</html>
Простой
