Ping event can't be Emitted or received

I used ws to implement my websocket server and in the api docs i found it has a ping/pong event,however, i couldn't received the event.
server:

wss.on("connection", function connection(ws) {
    ws.on('message', function(message) {
        console.log('received: %s', message);
    });
    ws.onclose = function () {
        console.log('client disappeared');
    };
    ws.ping('hello');//Send a ping
});

client:

<script>
        var ws = new WebSocket('ws://localhost:8080');

        function sendMesage() {
            ws.send('hello');
        }

        ws.onopen = function () {
            console.log('connection to server opened');
        };
        ws.onclose = function () {
            console.log('closed');
        }

        ws.onping = function () {
            console.log('ping');
        };// expect to receive ping event
    </script> 

via user7238980