htmx-ext-ws
v2.0.1
Published
The `WebSockets` extension enables easy, bi-directional communication with [Web Sockets](https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API/Writing_WebSocket_client_applications) servers directly from HTML. This replaces the experimental `hx-
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The WebSockets
extension enables easy, bi-directional communication
with Web Sockets
servers directly from HTML. This replaces the experimental hx-ws
attribute built into previous versions of htmx. For
help migrating from older versions, see the Migrating guide at the bottom of this page.
Use the following attributes to configure how WebSockets behave:
ws-connect="<url>"
orws-connect="<prefix>:<url>"
- A URL to establish aWebSocket
connection against.- Prefixes
ws
orwss
can optionally be specified. If not specified, HTMX defaults to adding the location's scheme-type, host and port to have browsers send cookies via websockets. ws-send
- Sends a message to the nearest websocket based on the trigger value for the element (either the natural event or the event specified by [hx-trigger
])
Install
<script src="https://unpkg.com/[email protected]/ws.js"></script>
Usage
<div hx-ext="ws" ws-connect="/chatroom">
<div id="notifications"></div>
<div id="chat_room">
...
</div>
<form id="form" ws-send>
<input name="chat_message">
</form>
</div>
Configuration
WebSockets extension support two configuration options:
createWebSocket
- a factory function that can be used to create a custom WebSocket instances. Must be a function, returningWebSocket
objectwsBinaryType
- a string value, that defines socket'sbinaryType
property. Default value isblob
Receiving Messages from a WebSocket
The example above establishes a WebSocket to the /chatroom
end point. Content that is sent down from the websocket
will
be parsed as HTML and swapped in by the id
property, using the same logic
as Out of Band Swaps.
As such, if you want to change the swapping method (e.g., append content at the end of an element or delegate swapping to an extension), you need to specify that in the message body, sent by the server.
<!-- will be interpreted as hx-swap-oob="true" by default -->
<form id="form">
...
</form>
<!-- will be appended to #notifications div -->
<div id="notifications" hx-swap-oob="beforeend">
New message received
</div>
<!-- will be swapped using an extension -->
<div id="chat_room" hx-swap-oob="morphdom">
....
</div>
Sending Messages to a WebSocket
In the example above, the form uses the ws-send
attribute to indicate that when it is submitted, the form values
should be serialized as JSON
and send to the nearest enclosing WebSocket
, in this case the /chatroom
endpoint.
The serialized values will include a field, HEADERS
, that includes the headers normally submitted with an htmx
request.
Automatic Reconnection
If the WebSocket is closed unexpectedly, due to Abnormal Closure
, Service Restart
or Try Again Later
, this
extension will attempt to reconnect until the connection is reestablished.
By default, the extension uses a
full-jitter exponential-backoff algorithm that chooses a randomized
retry delay that grows exponentially over time. You can use a different algorithm by writing it
into htmx.config.wsReconnectDelay
. This function takes a single parameter, the number of retries, and returns the
time (in milliseconds) to wait before trying again.
// example reconnect delay that you shouldn't use because
// it's not as good as the algorithm that's already in place
htmx.config.wsReconnectDelay = function (retryCount) {
return retryCount * 1000 // return value in milliseconds
}
The extension also implements a simple queuing mechanism that keeps messages in memory when the socket is not in OPEN
state and sends them once the connection is restored.
Events
WebSockets extensions exposes a set of events that allow you to observe and customize its behavior.
Event - htmx:wsConnecting
{#htmx:wsConnecting}
This event is triggered when a connection to a WebSocket endpoint is being attempted.
Details
detail.event.type
- the type of the event ('connecting'
)
Event - htmx:wsOpen
{#htmx:wsOpen}
This event is triggered when a connection to a WebSocket endpoint has been established.
Details
detail.elt
- the element that holds the socket (the one withws-connect
attribute)detail.event
- the original event from the socketdetail.socketWrapper
- the wrapper around socket object
Event - htmx:wsClose
{#htmx:wsClose}
This event is triggered when a connection to a WebSocket endpoint has been closed normally.
You can check if the event was caused by an error by inspecting detail.event
property.
Details
detail.elt
- the element that holds the socket (the one withws-connect
attribute)detail.event
- the original event from the socketdetail.socketWrapper
- the wrapper around socket object
Event - htmx:wsError
{#htmx:wsError}
This event is triggered when onerror
event on a socket is raised.
Details
detail.elt
- the element that holds the socket (the one withws-connect
attribute)detail.error
- the error objectdetail.socketWrapper
- the wrapper around socket object
Event - htmx:wsBeforeMessage
{#htmx:wsBeforeMessage}
This event is triggered when a message has just been received by a socket, similar to htmx:beforeOnLoad
. This event
fires
before any processing occurs.
If the event is cancelled, no further processing will occur.
detail.elt
- the element that holds the socket (the one withws-connect
attribute)detail.message
- raw message contentdetail.socketWrapper
- the wrapper around socket object
Event - htmx:wsAfterMessage
{#htmx:wsAfterMessage}
This event is triggered when a message has been completely processed by htmx and all changes have been
settled, similar to htmx:afterOnLoad
.
Cancelling this event has no effect.
detail.elt
- the element that holds the socket (the one withws-connect
attribute)detail.message
- raw message contentdetail.socketWrapper
- the wrapper around socket object
Event - htmx:wsConfigSend
{#htmx:wsConfigSend}
This event is triggered when preparing to send a message from ws-send
element.
Similarly to htmx:configRequest
, it allows you to modify the message
before sending.
If the event is cancelled, no further processing will occur and no messages will be sent.
Details
detail.parameters
- the parameters that will be submitted in the requestdetail.unfilteredParameters
- the parameters that were found before filtering byhx-select
detail.headers
- the request headers. Will be attached to the body inHEADERS
property, if not falsydetail.errors
- validation errors. Will prevent sending and triggerhtmx:validation:halted
event if not emptydetail.triggeringEvent
- the event that triggered sendingdetail.messageBody
- raw message body that will be sent to the socket. Undefined, can be set to value of any type, supported by WebSockets. If set, will override default JSON serialization. Useful, if you want to use some other format, like XML or MessagePackdetail.elt
- the element that dispatched the sending (the one withws-send
attribute)detail.socketWrapper
- the wrapper around socket object
Event - htmx:wsBeforeSend
{#htmx:wsBeforeSend}
This event is triggered just before sending a message. This includes messages from the queue. Message can not be modified at this point.
If the event is cancelled, the message will be discarded from the queue and not sent.
Details
detail.elt
- the element that dispatched the request (the one withws-connect
attribute)detail.message
- the raw message contentdetail.socketWrapper
- the wrapper around socket object
Event - htmx:wsAfterSend
{#htmx:wsAfterSend}
This event is triggered just after sending a message. This includes messages from the queue.
Cancelling the event has no effect.
Details
detail.elt
- the element that dispatched the request (the one withws-connect
attribute)detail.message
- the raw message contentdetail.socketWrapper
- the wrapper around socket object
Socket wrapper
You may notice that all events expose detail.socketWrapper
property. This wrapper holds the socket
object itself and the message queue. It also encapsulates reconnection algorithm. It exposes a few members:
send(message, fromElt)
- sends a message safely. If the socket is not open, the message will be persisted in the queue instead and sent when the socket is ready.sendImmediately(message, fromElt)
- attempts to send a message regardless of socket state, bypassing the queue. May failqueue
- an array of messages, awaiting in the queue.
This wrapper can be used in your event handlers to monitor and manipulate the queue (e.g., you can reset the queue when
reconnecting), and to send additional messages (e.g., if you want to send data in batches).
The fromElt
parameter is optional and, when specified, will trigger corresponding websocket events from
specified element, namely htmx:wsBeforeSend
and htmx:wsAfterSend
events when sending your messages.
Testing with the Demo Server
Htmx includes a demo WebSockets server written in Node.js that will help you to see WebSockets in action, and begin bootstrapping your own WebSockets code. It is located in the /test/ws-sse folder of the htmx distribution. Look at /test/ws-sse/README.md for instructions on running and using the test server.
Migrating from Previous Versions
Previous versions of htmx used a built-in tag hx-ws
to implement WebSockets. This code has been migrated into an
extension instead. Here are the steps you need to take to migrate to this version:
| Old Attribute | New Attribute | Comments |
|-------------------------|----------------------|----------------------------------------------------------------------------------------------------------------------------------|
| hx-ws=""
| hx-ext="ws"
| Use the hx-ext="ws"
attribute to install the WebSockets extension into any HTML element. |
| hx-ws="connect:<url>"
| ws-connect="<url>"
| Add a new attribute ws-connect
to the tag that defines the extension to specify the URL of the WebSockets server you're using. |
| hx-ws="send"
| ws-send=""
| Add a new attribute ws-send
to mark any child forms that should send data to your WebSocket server |