makc9I,
найдите 3 отличия )))
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<script>
function showText(classname, data) {
document.getElementsByClassName(classname)[0].innerHTML = data;
}
</script>
</head>
<body>
<span class="freeseat"
onMouseOver = "showText('freeseat','бронь');"
onMouseOut = "showText('freeseat','свободно');" >свободно
</span>
</body>
</html>