actions.md

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Actions

Actions are how you handle DOM events in your controllers.

<div data-controller="gallery">
  <button data-action="click->gallery#next">…</button>
</div>

// controllers/gallery_controller.js
import { Controller } from "@hotwired/stimulus"

export default class extends Controller {
  next(event) {
    // …
  }
}

An action is a connection between:

• a controller method
• the controller's element
• a DOM event listener

Descriptors

The data-action value click->gallery#next is called an action descriptor. In this descriptor:

• click is the name of the DOM event to listen for
• gallery is the controller identifier
• next is the name of the method to invoke

Event Shorthand

Stimulus lets you shorten the action descriptors for some common element/event pairs, such as the button/click pair above, by omitting the event name:

<button data-action="gallery#next">…</button>

The full set of these shorthand pairs is as follows:

Element	Default Event
a	click
button	click
details	toggle
form	submit
input	input
input type=submit	click
select	change
textarea	input

KeyboardEvent Filter

There may be cases where KeyboardEvent Actions should only call the Controller method when certain keystrokes are used.

You can install an event listener that responds only to the Escape key by adding .esc to the event name of the action descriptor, as in the following example.

<div data-controller="modal"
     data-action="keydown.esc->modal#close" tabindex="0">
</div>

This will only work if the event being fired is a keyboard event.

The correspondence between these filter and keys is shown below.

Filter	Key Name
enter	Enter
tab	Tab
esc	Escape
space	" "
up	ArrowUp
down	ArrowDown
left	ArrowLeft
right	ArrowRight
home	Home
end	End
page_up	PageUp
page_down	PageDown
[a-z]	[a-z]
[0-9]	[0-9]

If you need to support other keys, you can customize the modifiers using a custom schema.

import { Application, defaultSchema } from "@hotwired/stimulus"

const customSchema = {
  ...defaultSchema,
  keyMappings: { ...defaultSchema.keyMappings, at: "@" },
}

const app = Application.start(document.documentElement, customSchema)

If you want to subscribe to a compound filter using a modifier key, you can write it like ctrl+a.

<div data-action="keydown.ctrl+a->listbox#selectAll" role="option" tabindex="0">...</div>

The list of supported modifier keys is shown below.

Modifier	Notes
alt	option on MacOS
ctrl
meta	Command key on MacOS
shift

Global Events

Sometimes a controller needs to listen for events dispatched on the global window or document objects.

You can append @window or @document to the event name (along with any filter modifier) in an action descriptor to install the event listener on window or document, respectively, as in the following example:

<div data-controller="gallery"
     data-action="resize@window->gallery#layout">
</div>

Options

You can append one or more action options to an action descriptor if you need to specify DOM event listener options.

<div data-controller="gallery"
     data-action="scroll->gallery#layout:!passive">
  <img data-action="click->gallery#open:capture">

Stimulus supports the following action options:

Action option	DOM event listener option
:capture	{ capture: true }
:once	{ once: true }
:passive	{ passive: true }
:!passive	{ passive: false }

On top of that, Stimulus also supports the following action options which are not natively supported by the DOM event listener options:

Custom action option	Description
:stop	calls .stopPropagation() on the event before invoking the method
:prevent	calls .preventDefault() on the event before invoking the method
:self	only invokes the method if the event was fired by the element itself

You can register your own action options with the Application.registerActionOption method.

For example, consider that a <details> element will dispatch a toggle event whenever it's toggled. A custom :open action option would help to route events whenever the element is toggled open:

import { Application } from "@hotwired/stimulus"

const application = Application.start()

application.registerActionOption("open", ({ event }) => {
  if (event.type == "toggle") {
    return event.target.open == true
  } else {
    return true
  }
})

Similarly, a custom :!open action option could route events whenever the element is toggled closed. Declaring the action descriptor option with a ! prefix will yield a value argument set to false in the callback:

import { Application } from "@hotwired/stimulus"

const application = Application.start()

application.registerActionOption("open", ({ event, value }) => {
  if (event.type == "toggle") {
    return event.target.open == value
  } else {
    return true
  }
})

In order to prevent the event from being routed to the controller action, the registerActionOption callback function must return false. Otherwise, to route the event to the controller action, return true.

The callback accepts a single object argument with the following keys:

Name	Description
name	String: The option's name ("open" in the example above)
value	Boolean: The value of the option (:open would yield true, :!open would yield false)
event	Event: The event instance, including with the params action parameters on the submitter element
element	Element: The element where the action descriptor is declared
controller	The Controller instance which would receive the method call

Event Objects

An action method is the method in a controller which serves as an action's event listener.

The first argument to an action method is the DOM event object. You may want access to the event for a number of reasons, including:

• to read the key code from a keyboard event
• to read the coordinates of a mouse event
• to read data from an input event
• to read params from the action submitter element
• to prevent the browser's default behavior for an event
• to find out which element dispatched an event before it bubbled up to this action

The following basic properties are common to all events:

Event Property	Value
event.type	The name of the event (e.g. "click")
event.target	The target that dispatched the event (i.e. the innermost element that was clicked)
event.currentTarget	The target on which the event listener is installed (either the element with the data-action attribute, or document or window)
event.params	The action params passed by the action submitter element

The following event methods give you more control over how events are handled:

Event Method	Result
event.preventDefault()	Cancels the event's default behavior (e.g. following a link or submitting a form)
event.stopPropagation()	Stops the event before it bubbles up to other listeners on parent elements

Multiple Actions

The data-action attribute's value is a space-separated list of action descriptors.

It's common for any given element to have many actions. For example, the following input element calls a field controller's highlight() method when it gains focus, and a search controller's update() method every time the element's value changes:

<input type="text" data-action="focus->field#highlight input->search#update">

When an element has more than one action for the same event, Stimulus invokes the actions from left to right in the order that their descriptors appear.

The action chain can be stopped at any point by calling Event#stopImmediatePropagation() within an action. Any additional actions to the right will be ignored:

highlight(event) {
  event.stopImmediatePropagation()
  // ...
}

Naming Conventions

Always use camelCase to specify action names, since they map directly to methods on your controller.

Avoid action names that simply repeat the event's name, such as click, onClick, or handleClick:

<button data-action="click->profile#click">Don't</button>

Instead, name your action methods based on what will happen when they're called:

<button data-action="click->profile#showDialog">Do</button>

This will help you reason about the behavior of a block of HTML without having to look at the controller source.

Action Parameters

Actions can have parameters that are be passed from the submitter element. They follow the format of data-[identifier]-[param-name]-param. Parameters must be specified on the same element as the action they intend to be passed to is declared.

All parameters are automatically typecast to either a Number, String, Object, or Boolean, inferred by their value:

Data attribute	Param	Type
data-item-id-param="12345"	12345	Number
data-item-url-param="/votes"	"/votes"	String
data-item-payload-param='{"value":"1234567"}'	{ value: 1234567 }	Object
data-item-active-param="true"	true	Boolean

Consider this setup:

<div data-controller="item spinner">
  <button data-action="item#upvote spinner#start" 
    data-item-id-param="12345" 
    data-item-url-param="/votes"
    data-item-payload-param='{"value":"1234567"}' 
    data-item-active-param="true">…</button>
</div>

It will call both ItemController#upvote and SpinnerController#start, but only the former will have any parameters passed to it:

// ItemController
upvote(event) {
  // { id: 12345, url: "/votes", active: true, payload: { value: 1234567 } }
  console.log(event.params) 
}

// SpinnerController
start(event) {
  // {}
  console.log(event.params) 
}

If we don't need anything else from the event, we can destruct the params:

upvote({ params }) {
  // { id: 12345, url: "/votes", active: true, payload: { value: 1234567 } }
  console.log(params) 
}

Or destruct only the params we need, in case multiple actions on the same controller share the same submitter element:

upvote({ params: { id, url } }) {
  console.log(id) // 12345
  console.log(url) // "/votes"
}