HTMX、WebSocket、Hono でチャットする

Last week, I wrote about tweaking htmx to display instant messages. A week into using HTMX, I needed more. I wanted a better way to stream HTML from the server, using JSX components instead of plain HTML strings for better code usability.

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Tools I Used:

• HTMX
• HTMX Websockets Extension
• Hono for the backend
• Websockets - client-side

The idea is simple. My Conversation component is wrapped in a div with hx-ext="ws", which connects to my backend when rendered.

export const Conversation = (props: { messages: Message[] }) => (
  <div hx-ext="ws" ws-connect="/chatroom-ws">
      <div id="conversation">
        {props.messages.reverse().map((message) => (
          <div>
            <usermessage message="{message}"></usermessage>
            <assistantmessage message="{message}"></assistantmessage>
          </div>
        ))}
      </div>
      <inputmessageform></inputmessageform>
  </div>
);

Next important thing is the InputMessageForm. Just add ws-send to the form, and it will send a message where the key is the textarea’s ID (messageInput) with its value.

export const InputMessageForm = () => (
  

Send

);

Websockets - Server

Here’s the full code block for the Hono server. Some console logs for opening and closing connection. onMessage is where the magic happens.

get(
    '/chatroom-ws',
    upgradeWebSocket((c) => {
      return {
        onOpen: () => {
          console.log('WS Connection open');
        },
        onClose: () => {
          console.log('WS Connection closed');
        },
        onMessage: async (event, ws) => {
          const { userMessage } = JSON.parse(event.data.toString());
          console.log('Got user message', userMessage);
          const inputArea = await c.html(
            <div id="query-submit-form">
              <inputmessageform></inputmessageform>
            </div>,
          );
          ws.send(await inputArea.text());
          const htmlUser = await c.html(
            <div id="conversation" hx-swap-oob="beforeend">
              <usermessage message="{{" id: v4 some random ids used here for placeholder query: usermessage completion: conversationid: toolsresponse: null createdat: new date updatedat:></usermessage>
            </div>,
          );
          ws.send(await htmlUser.text());
          const response = await talk(userMessage);
          const htmlAgent = await c.html(
            <div id="conversation" hx-swap-oob="beforeend">
              <assistantmessage message="{response}"></assistantmessage>
            </div>,
          );
          ws.send(await htmlAgent.text());
        },
      };
    }),
);

So the flow is:

1. Receive the query
2. Send back empty just to make it clean. There is no hx-swap-oob specified so its True by default. That means that it will find the element with id=query-submit-form and swap it.
3. Send back the component with the user message. Here hx-swap-oob is specified to beforeend which simply means that it will be added to existing messages.
4. talk → here comes your logic. I’m talking to AI assistant so making some external API calls.
5. Send back the component with assistant answer. The same as step 3 but the component is different.

Problems I found

Sending response back was a bit problematic since docs are hmm… not that easy to understand I think. There is even an issue created to fix this: Improve documentation for websocket extension. That helped me a lot!

So the most important thing is:

You need to send back string, that parses to html that has the same id as the thing you want to swap!

So the problem nr. 1

I accidentally sent back something like this:

JSON.stringify('<div id="someid">test 123</div>')
// '"<div id='\\"someid\\"'>test 123</div>"'

This is wrong. Note the ID and escape characters! Don’t stringify the string here.

The problem nr. 2

You might think you can return something and it will get swapped where you want. Not exactly. The first div is just information for HTMX on what to do. At least I understand it this way ?.

I’m returning html like this:

<div id="conversation" hx-swap-oob="beforeend">
      <assistantmessage message="{response}"></assistantmessage>
</div>

Only  is appended inside the existing 

 on the client side.

End result

https://assets.super.so/c0fc84d8-fb32-4194-8758-4be657666aab/videos/c814dcd2-b9e9-4bb2-b8db-2ed9cd7819b7/lucy-chat-example.mov

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