<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>ボタン</title>
</head>
<body>

<p>ボタン</p>

<button id="btn01">クリックしてね</button>
</body>
<script>
	var btn01 = document.getElementById("btn01");
	btn01.addEventListener("click", sw, false);

function sw() {
	btn01.textContent ="changed.";
}


	
</script>
</html>