Migor,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.item {
display: none;
}
.item.open {
display: block;
}
</style>
<script>
document.addEventListener("DOMContentLoaded", function() {
let url = new URL('https://my-site/home?tab=2'); //let url = new URL(location);
let index = new URLSearchParams(url.search).get('tab') || 0;
let elems = document.querySelectorAll(".item");
elems[index].classList.add("open")
})
</script>
</head>
<body>
<div class="item">0</div>
<div class="item">1</div>
<div class="item">2</div>
</body>
</html>