Lifecycle

How to hook into Reflex activity... aka callbacks

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

  • You can abort a Reflex - prevent it from executing - by placing throw :abort in a before_reflex callback. An aborted Reflex will trigger the halted life-cycle stage on the client.

class ExampleReflex < StimulusReflex::Reflex
# 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

Client-Side Reflex Callbacks

StimulusReflex gives you the ability to inject custom JavaScript at five distinct moments around sending an event to the server and updating the DOM. These hooks allow you to improve the user experience and handle edge cases.

  1. before prior to sending a request over the web socket

  2. success after the server side Reflex succeeds and the DOM has been updated

  3. error whenever the server side Reflex raises an error

  4. halted Reflex canceled by developer with throw :abort in the before_reflex callback

  5. after follows either success or error immediately before DOM manipulations

  6. finalize occurs immediately after all DOM manipulations are complete

Using lifecycle callback methods is not a requirement.

Think of them as power tools that can help you build more sophisticated results. 👷

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.

StimulusReflex also emits lifecycle events which can be captured in other Stimulus controllers, jQuery plugins or even the console.

Generic Lifecycle Methods

StimulusReflex controllers automatically support five generic lifecycle 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

While this is perfect for simpler Reflexes with a small number of actions, most developers quickly switch to using Custom Lifecycle Methods, which allow you to define different callbacks for every action.

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

app/views/examples/show.html.erb
<div data-controller="example">
<a href="#" data-reflex="Example#masticate">Eat</a>
<a href="#" data-reflex="Example#deficate">Poop</a>
</div>
app/javascript/controllers/example_controller.js
import ApplicationController from './application_controller.js'
export default class extends ApplicationController {
beforeReflex(anchorElement) {
const { reflex } = anchorElement.dataset
if (reflex.match(/masticate$/)) anchorElement.innerText = 'Eating...'
if (reflex.match(/deficate$/)) anchorElement.innerText = 'Pooping...'
}
}

Custom Lifecycle Methods

StimulusReflex controllers can define up to five custom lifecycle 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 lifecycle callback methods:

  1. beforePoke

  2. pokeSuccess

  3. pokeError

  4. pokeHalted

  5. afterPoke

  6. finalizePoke

app/views/examples/show.html.erb
<div data-controller="example">
<a href="#" data-reflex="Example#poke">Poke</a>
<a href="#" data-reflex="Example#purge">Purge</a>
</div>
app/javascript/controllers/example_controller.js
import ApplicationController from './application_controller.js'
export default class extends ApplicationController {
beforePoke(anchorElement) {
anchorElement.innerText = 'Poking...'
}
beforePurge(anchorElement) {
anchorElement.innerText = 'Purging...'
}
}

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

It's not required to implement all lifecycle methods. Pick and choose which lifecycle callback methods make sense for your application. The answer is frequently none.

Adding a declarative Reflex such as Foo#action to your element does not automatically attach an instance of the foo Stimulus controller to the element.

This coupling would only add an unneccessary constraint, as you can call any Reflex from any Stimulus controller.

If you want to run Reflex lifecycle callbacks on your element, you need to use data-controller="foo" to attach it.

You can use both data-reflex and data-controller at the same time.

Conventions

Method Names

Lifecycle callback methods apply a naming convention based on your Reflex actions. For example, the Reflex ExampleReflex#do_stuff will produce the following camel-cased lifecycle callback methods.

  1. beforeDoStuff

  2. doStuffSuccess

  3. doStuffError

  4. doStuffHalted

  5. afterDoStuff

  6. finalizeDoStuff

Method Signatures

Both generic and custom lifecycle 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

Lifecycle Events

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 lifecycle; 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 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.

Knowing which element dispatched the event might appear daunting, but the key is in knowing how the Reflex was created. If a Reflex is declared using a data-reflex attribute in your HTML, the event will be emitted by the element with the attribute.

If you're calling the stimulate method inside of a Stimulus controller, the event will be emitted by the element the data-controller attribute is declared on.

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.

Promises

Are you a hardcore JavaScript developer? A props power-lifter? Then you'll be pleased to know that in addition to lifecycle methods and events, StimulusReflex allows you to write promise resolver functions:

this.stimulate('Comments#create')
.then(() => this.doSomething())
.catch(() => this.handleError())

You can get a sense of the possibilities:

this.stimulate('Post#publish')
.then(payload => {
const { data, element, event } = payload
const { attrs, reflexId } = data
// * attrs - an object that represents the attributes of the element that triggered the reflex
// * 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
// * reflexId - a unique identifier for this specific reflex invocation
})
.catch(payload => {
const { data, element, event } = payload
const { attrs, reflexId } = data
const { error } = event.detail.stimulusReflex
// * attrs - an object that represents the attributes of the element that triggered the reflex
// * 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
// * error - the error message from the server
// * event - the source event
// * reflexId - a unique identifier for this specific reflex invocation
})

You can get the reflexId of an unresolved promise:

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

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 lifecycle 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:connected

  • stimulus-reflex:disconnected

  • stimulus-reflex:rejected

  • stimulus-reflex:ready

All four events fire on document.

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.