Life-cycle ​

Server-Side Reflex Callbacks ​

StimulusReflex gives you a set of callback events to control how your Reflex actions function. These usual suspects will be familiar to Rails developers:

• before_reflex, around_reflex , after_reflex
• All callbacks can receive multiple symbols representing Reflex actions, an optional block and the following options: only, except, if, unless

class ExampleReflex < ApplicationReflex
  # will run only if the element has the step attribute, can use "unless" instead of "if" for opposite condition
  before_reflex :do_stuff, if: proc { |reflex| reflex.element.dataset.step }

  # will run only if the reflex instance has a url attribute, can use "unless" instead of "if" for opposite condition
  before_reflex :do_stuff, if: :url

  # will run before all reflexes
  before_reflex :do_stuff

  # will run before increment reflex, can use "except" instead of "only" for opposite condition
  before_reflex :do_stuff, only: [:increment]

  # will run around all reflexes, must have a yield in the callback
  around_reflex :do_stuff_around

 # will run after all reflexes
  after_reflex :do_stuff

  # Example with a block
  before_reflex do
    # callback logic
  end

  # Example with multiple method names
  before_reflex :do_stuff, :do_stuff2

  # Example with halt
  before_reflex :run_checks

  def increment
    # reflex logic
  end

  def decrement
    # reflex logic
  end

  private

  def run_checks
    throw :abort # this will prevent the Reflex from continuing
  end

  def do_stuff
    # callback logic
  end

  def do_stuff2
    # callback logic
  end

  def do_stuff_around
    # before
    yield
    # after
  end
end

Aborting a Reflex ​

It is possible that you might want to abort a Reflex and prevent it from executing. For example, the user might not have appropriate permissions to complete an action, or perhaps some other side effect like missing data would cause an exception if the Reflex was allowed to continue.

An aborted Reflex will trigger the halted life-cycle stage instead of the after and finalize stages on the client. You can learn more about how aborted Reflexes behave in different scenarios in Understanding Stages.

To abort a Reflex, call throw :abort inside of a before_reflex callback on your Reflex class.

Client-Side Reflex Callbacks ​

StimulusReflex gives you the ability to inject custom JavaScript at distinct moments around the life-cycle of a Reflex. Developers can use a combination of callback methods, event handlers and Promise resolution to improve the user experience and handle edge cases.

1. before prior to sending a Reflex over the WebSocket
2. success after the server-side Reflex processes successfully
3. error after the server-side Reflex raises an error
4. halted Reflex canceled by developer with throw :abort in a before_reflex callback
5. after follows either success or error immediately before DOM manipulations
6. finalize occurs immediately after all DOM manipulations are complete

Order of operations ​

The order of operations for life-cycle management techniques is:

1. Promise resolution
2. Callback methods
3. Event handlers

There is no "best" way to handle life-cycle stages, and most developers use a blend of the available tools depending on the situation and their preferred development style. While the APIs are different, we've worked hard to make sure that each mechanism has access to all of the Reflex data available at each stage of the process.

Understanding Stages ​

Most of the time, it's reasonable to expect that your Reflexes will follow a predictable cycle: before -> success -> after -> finalize.

There are, however, several important exceptions to the norm.

1. Reflexes that are aborted on the server have a short cycle: before -> halted
2. Reflexes that have errors: before -> error -> after -> [finalize]
3. Nothing Morphs end early: before -> [success] -> after
4. Event handlers for the after stage will fire before success and error.
5. Nothing Morphs have no CableReady operations to wait for, so there is nothing to finalize.
6. Nothing Morphs support success callback methods but do not emit success events.
7. A Reflex with an error will not have a finalize stage.

Callback Methods ​

If you define a method with a name that matches what the library searches for, it will run at just the right moment. If there's no method defined, nothing happens. StimulusReflex will only look for these methods in Stimulus controllers that extend ApplicationController or have called StimulusReflex.register(this) in their connect() function.

There are two kinds of callback methods: generic and custom. Generic callback methods are invoked for every Reflex action on a controller. Custom callback methods are only invoked for specific Reflex actions.

Generic Life-cycle Methods ​

StimulusReflex controllers automatically support generic life-cycle callback methods. These methods fire for every Reflex action handled by the controller.

1. beforeReflex
2. reflexSuccess
3. reflexError
4. reflexHalted
5. afterReflex
6. finalizeReflex

In this example, we update each anchor's text before invoking the server side Reflex:

<div data-controller="example">
  <a href="#" data-reflex="Example#masticate">Eat</a>
  <a href="#" data-reflex="Example#defecate">Poop</a>
</div>

import ApplicationController from './application_controller.js'

export default class extends ApplicationController {
  beforeReflex(anchorElement) {
    const { reflex } = anchorElement.dataset
    if (reflex.match(/masticate$/)) anchorElement.innerText = 'Eating...'
    if (reflex.match(/defecate$/)) anchorElement.innerText = 'Pooping...'
  }
}

Custom Life-cycle Methods ​

StimulusReflex controllers can define up to six custom life-cycle callback methods for each Reflex action. These methods use a naming convention based on the name of the Reflex. The naming follows the pattern <actionName>Success and matches the camelCased name of the action.

The Reflex Example#poke will cause StimulusReflex to check for the existence of the following life-cycle callback methods:

1. beforePoke
2. pokeSuccess
3. pokeError
4. pokeHalted
5. afterPoke
6. finalizePoke

<div data-controller="example">
  <a href="#" data-reflex="click->Example#poke">Poke</a>
  <a href="#" data-reflex="click->Example#purge">Purge</a>
</div>

import ApplicationController from './application_controller.js'

export default class extends ApplicationController {
  beforePoke(element) {
    element.innerText = 'Poking...'
  }

  beforePurge(element) {
    element.innerText = 'Purging...'
  }
}

Adapting the Generic example, we've refactored our controller to execute the before callback methods for each anchor individually.

Method Names ​

Life-cycle callback methods apply a naming convention based on your Reflex actions. For example, the Reflex ExampleReflex#do_stuff will search for the following camel-cased life-cycle callback methods.

1. beforeDoStuff
2. doStuffSuccess
3. doStuffError
4. doStuffHalted
5. afterDoStuff
6. finalizeDoStuff

Method Signatures ​

Both generic and custom life-cycle callback methods share the same arguments:

• beforeReflex(element, reflex, noop, reflexId)
• reflexSuccess(element, reflex, noop, reflexId)
• reflexError(element, reflex, error, reflexId)
• reflexHalted(element, reflex, noop, reflexId)
• afterReflex(element, reflex, noop, reflexId)
• finalizeReflex(element, reflex, noop, reflexId)

element - the DOM element that triggered the Reflex this may not be the same as the controller's this.element

reflex - the name of the server side Reflex

error/noop - the error message (for reflexError), otherwise null

reflexId - a UUID4 or developer-provided unique identifier for each Reflex

Life-cycle Events/Event Handlers ​

If you need to know when a Reflex method is called, but you're working outside of the Stimulus controller that initiated it, you can subscribe to receive DOM events.

DOM events are limited to the generic life-cycle; developers can obtain information about which Reflex methods were called by inspecting the detail object when the event is captured.

Events are dispatched on the same element that triggered the Reflex. Events bubble but cannot be cancelled.

Event Names ​

• stimulus-reflex:before
• stimulus-reflex:success
• stimulus-reflex:error
• stimulus-reflex:halted
• stimulus-reflex:after
• stimulus-reflex:finalize

Event Metadata ​

When an event is captured, you can obtain all of the data required to respond to a Reflex action:

document.addEventListener('stimulus-reflex:before', event => {
  event.target // the element that triggered the Reflex (may not be the same as controller.element)
  event.detail.reflex // the name of the invoked Reflex
  event.detail.reflexId // the UUID4 or developer-provided unique identifier for each Reflex
  event.detail.controller // the controller that invoked the stimuluate method
  event.target.reflexData[event.detail.reflexId] // the data payload that will be delivered to the server
  event.target.reflexData[event.detail.reflexId].params // the serialized form data for this Reflex
})

event.target is a reference to the element that triggered the Reflex, and event.detail.controller is a reference to the instance of the controller that called the stimulate method. This is especially handy if you have multiple instances of a controller on your page.

jQuery Events ​

In addition to DOM events, StimulusReflex will also emits duplicate jQuery events which you can capture. This occurs only if the jQuery library is present in the global scope eg. available on window.

These jQuery events have the same name and details accessors as the DOM events.

Promise Resolution ​

In addition to life-cycle methods and events, StimulusReflex allows you to write promise resolver functions:

this.stimulate('Comments#create')
  .then(this.handleSuccess)
  .catch(this.handleError)

You can get a sense of the possibilities:

this.stimulate('Post#publish').then(promise => {
  const { data, element, event, payload, reflexId } = promise
  // * data - the data sent from the client to the server over the web socket to invoke the reflex
  // * element - the element that triggered the reflex
  // * event - the source event
  // * payload - optional return data passed from the Reflex method
  // * reflexId - a unique identifier for this specific reflex invocation
}).catch(promise => {
  const { data, element, event, payload, reflexId, error } = promise
  // * error - the error message from the server
})

You can get the reflexId of an unresolved promise:

const snail = this.stimulate('Snail#secrete')
console.log(snail.reflexId)
snail.then(trail => console.log)

Configuring Promise resolution timing ​

Any Promise can only be resolved once, at which time your callback will run if defined. By default, StimulusReflex will resolve the Promise associated with a Reflex action during the after life-cycle stage. This means your callback will execute after the server has executed the Reflex action but before any DOM modifications are initiated. In some cases, this is too soon to be useful.

You can initiate a Reflex that will resolve its Promise during the finalize life-cycle stage, after all CableReady operations have completed. At this point, all DOM modifications are complete and it is safe to initiate animations or other effects.

To request that a Reflex resolve its Promise during the finalize stage instead of after, pass resolveLate: true as one of the possible optional arguments to the stimulate method.

this.stimulate('Example#foo', { resolveLate: true }).then(() => {
  console.log('The Reflex has been finalized.')
})

StimulusReflex Library Events ​

In addition to the Reflex life-cycle mechanisms, the StimulusReflex client library emits its own set of handy DOM events which you can hook into and use in your applications.

• stimulus-reflex:action-cable:connected
• stimulus-reflex:action-cable:disconnected
• stimulus-reflex:action-cable:rejected
• stimulus-reflex:ready

In previous versions, ActionCable was assumed; in future versions of the library, other transport mechanisms will be available. Legacy library events are now deprecated and will be removed in the future:

• stimulus-reflex:connected
• stimulus-reflex:disconnected
• stimulus-reflex:rejected

All events fire on document, except stimulus-reflex:ready which is being dispatched on the StimulusReflex controller element itself.

connected fires when the ActionCable connection is established, which is a precondition of a successful call to stimulate - meaning that you can delay calls until the event arrives. It will also fire after a disconnected subscription is reconnected.

disconnected fires if the connection to the server is lost; the detail object of the event has a willAttemptReconnect boolean which should be true in most cases.

rejected is fired if you're doing authentication in your Channel and the subscription request was denied.

ready is slightly different than the first three, in that it has nothing to do with the ActionCable subscription. Instead, it is called after StimulusReflex has scanned your page, looking for declared Reflexes to connect. This event fires every time the document body is modified, and was created primarily to support automated JS test runners like Cypress. Without this event, Cypress tests would have to wait for a few seconds before "clicking" on Reflex-enabled UI elements.

jQuery Events ​

In addition to DOM events, StimulusReflex will also emits duplicate jQuery events which you can capture. This occurs only if the jQuery library is present in the global scope eg. available on window.

These jQuery events have the same name and details accessors as the DOM events.