WebSocket - get state of single entity

Configuration
1

Does WebSocket API have a way of retrieving state of the single entity?

From what I see, it only has a way of retrieving all entities at once which is a bit overkill for my taste.

2

Maybe this helps.

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <script src='http://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js'></script>
    <script type="text/javascript">
        var myentity;
        function getvalue() {
        $(document).ready(function () {
            function msg(str) {
                $('#msg').append('<p>' + str + '</p>');
            };
            ws = new WebSocket('wss://youraddress/api/websocket');
            ws.addEventListener('open', function (event) {
                ws.send(JSON.stringify({"type": "auth","access_token": "yourtoken"}))
                ws.send('{"id": 1, "type": "get_states"}\n');
            });
            ws.onmessage = function(event) {
                //this if removes other messages comming from the websocket (e.g. auth ok)
                if (event.data.length > 2000) {
                window.myentity = JSON.parse(event.data)["result"].filter(function (el) { return el.entity_id == "sun.sun"})[0].state;
                msg(myentity);
                ws.close();
                }
            };
            ws.onopen = function() {msg('Connected...');};
            ws.onclose = function() {msg('Socket closed');};
        });
        }
    </script>
</head>
<body onload="getvalue()">
<button onclick="getvalue()">Get new value</button>
<div id="msg"></div>
</body>
</html>
3

No, this uses get_states which fetches all states and then filters them out on the client side.

4

From what I read on the official page (I didn’t dig too much in the code) you can’t access a single entity - using the current options for the HASS WebSocket API. You either get them all and filter them (as I do) or keep an event subscription open and filter the incoming messages.
You can use the REST API. With that one you can access a single entity easily.

5

Looking at the source code of version 2023.11.2 in /components/websocket_api/commands.py this is possible.
There is a (currently) undocumented websocket command of ‘subscribe_entities’.
I’ve tested with the following websocket command it provides state updates for a limited set of entities.

{ “id”: 18,
“type”: “subscribe_entities”,
“entity_ids”: [“switch.test_lamp”]
}

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