<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Document</title>
<script>
function handler(i)
{
alert("нажали кнопку");
}
</script>
</head>
<body>
<input type="button" name="b" value="Press me" onclick="handler(this)"/>
</body>
</html>
Простой