Hi!!!
Thank you for helping.
With:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"/>
<title>y-webrtc demo</title>
</head>
<body>
<button type="button" id="y-connect-btn">Disconnect</button>
<script type="text/javascript" src="./client.js"></script>
</body>
It seems fine actually now. Thank you!
I opened an another question here: `y-webrtc` : WebSocket connection failed : 'wss://y-webrtcsignaling-eu.herokuapp.com'