よく見かけるタブ切替えではなく,ドロップダウン切替えを作ってみた.特徴は,<select>タグや<option>タグを使わず,Bootstrapで作ったので,多少見栄えが良いところ.
<!DOCTYPE html>
<head>
<meta charset="utf-8">
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css">
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.0/umd/popper.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
</head>
<body>
<div class="dropdown inline">
<button class="btn btn-secondary dropdown-toggle" type="button" id="grade" data-toggle="dropdown">
1年
</button>
<div class="dropdown-menu" aria-labelledby="grade">
<a id="02" class="dropdown-item" href="#">2年</a>
<a id="03" class="dropdown-item" href="#">3年</a>
<a id="04" class="dropdown-item" href="#">4年</a>
</div>
</div>
<div id="class" class="inline">
<button class="btn">1組</button>
</div>
<script>
$(function(){
$('#02').click(function(){
$('#grade').text('2年');
$('#class').empty();
$('#class').append('<button class="btn">1組</button><button class="btn">2組</button><button class="btn">3組</button>');
})
$('#03').click(function(){
$('#grade').text('3年');
$('#class').empty();
$('#class').append('<button class="btn">1組</button><button class="btn">2組</button>');
})
$('#04').click(function(){
$('#grade').text('4年');
$('#class').empty();
$('#class').append('<button class="btn">A組</button><button class="btn">B組</button>');
})
});
</script>
<style>
.inline
{
display: inline;
}
</style>
</body>
</html>