htmx Events Guide

Listen for htmx events to log, cancel, and modify request and swap behavior.

htmx triggers events at every step of the request and swap lifecycle. These events are the main extension point for scripting htmx. You can use them to log what htmx does, to cancel an action, or to change it before it happens.

Listening For Events

There are three ways to listen for an htmx event.

Use htmx.on(), which listens on document by default:

htmx.on('htmx:after:swap', function (evt) {
    console.log('swapped', evt.detail.ctx.target);
});

Use the standard addEventListener:

document.body.addEventListener('htmx:after:init', function (evt) {
    setUpElement(evt.detail.elt);
});

Or use an hx-on:* attribute on the element itself:

<button hx-post="/example"
        hx-on:htmx:config:request="ctx.request.body.set('source', 'button')">
    Post Me!
</button>

htmx events bubble, so a listener on document or document.body sees events from every element. Use an hx-on:* attribute when you only want to handle events from one element.

The Event Detail

Most htmx events carry a detail object. For request and swap events, detail.ctx is the request context. It holds the source element, the target, the swap style, the request, and, after the response arrives, the response.

htmx.on('htmx:before:request', function (evt) {
    let ctx = evt.detail.ctx;
    console.log(ctx.request.method, ctx.request.action, ctx.target);
});

Inside an hx-on:* attribute every property of detail is already in scope, so you write ctx rather than event.detail.ctx.

Element lifecycle events use detail.elt instead, which is the element htmx processed.

Cancelling An Event

htmx events are cancelable. Call preventDefault() to stop htmx from continuing:

htmx.on('htmx:before:request', function (evt) {
    if (!isLoggedIn()) {
        evt.preventDefault();
    }
});

Cancelling has a different effect for each event:

Event	Effect of cancelling
`htmx:confirm`	suppresses the built-in confirmation. Call `detail.issueRequest()` or `detail.dropRequest()` yourself
`htmx:before:request`	the request is never sent
`htmx:before:response`	the response body is never read and no swap happens
`htmx:after:request`	the response is read but no swap happens
`htmx:before:swap`	no swap task runs
`htmx:before:init`	the element is not initialized
`htmx:before:process`	the node and its descendants are not processed

The Event Lifecycle

Request Events

These events fire in order for every request.

Event	When it fires
`htmx:confirm`	before htmx handles `hx-confirm`
`htmx:config:request`	before the request data is encoded. Change `ctx.request` here
`htmx:before:request`	immediately before `fetch()`
`htmx:before:response`	after `fetch()`, before the body is read
`htmx:after:request`	after the response body is read
`htmx:response:error`	the response status is 400 or higher
`htmx:error`	a request or swap threw an exception
`htmx:finally:request`	the lifecycle ended, including on failure

Swap Events

Event	When it fires
`htmx:before:swap`	before the DOM is updated. `detail.tasks` holds the planned swaps
`htmx:before:settle`	after insertion, before the settle tasks
`htmx:after:settle`	after the settle tasks
`htmx:after:swap`	after the DOM is updated
`htmx:finally:swap`	at the end of the swap lifecycle
`htmx:before:viewTransition`	before a view transition starts
`htmx:after:viewTransition`	after a view transition completes

Element Lifecycle Events

Event	When it fires
`htmx:before:process`	before htmx processes a DOM node
`htmx:after:process`	after htmx processes a DOM node
`htmx:before:init`	before an element is initialized
`htmx:after:init`	after an element is initialized
`htmx:before:cleanup`	before htmx removes its data from an element
`htmx:after:cleanup`	after htmx removes its data from an element

History Events

Event	When it fires
`htmx:before:history:update`	before the browser history is updated
`htmx:after:history:update`	after the browser history is updated
`htmx:after:history:push`	after a URL is pushed
`htmx:after:history:replace`	after a URL is replaced
`htmx:before:history:restore`	before a page is restored from history

See the events reference for the full list, including the trigger events load, intersect and every.

Common Recipes

Initialize A Third Party Library

New content that htmx swaps in is not known to your other libraries. Listen for htmx:after:init to set it up:

htmx.on('htmx:after:init', function (evt) {
    setUpElement(evt.detail.elt);
});

You can also use htmx.onLoad(), which is a shorthand for this.

Add A Value To Every Request

htmx:config:request fires before the request body is encoded, so ctx.request.body is still a FormData object:

htmx.on('htmx:config:request', function (evt) {
    evt.detail.ctx.request.body.set('csrf-token', getToken());
});

To add a header instead, write to ctx.request.headers:

htmx.on('htmx:config:request', function (evt) {
    evt.detail.ctx.request.headers['X-CSRF-Token'] = getToken();
});

Change The Target Or Swap Style

Both are on the context, so you can change them up to the point of the swap:

htmx.on('htmx:before:swap', function (evt) {
    if (evt.detail.ctx.response.status === 404) {
        evt.detail.ctx.target = document.querySelector('#errors');
    }
});

For the declarative version of this, see hx-status.

Logging Events

Set htmx.config.logAll to true to log every htmx event to the console:

htmx.config.logAll = true;

You can also set it from HTML:

<meta name="htmx-config" content="logAll:true">

htmx always logs events whose detail carries an error at error level, and events whose detail carries a warn at warning level. logAll adds everything else.