# Lifecycle
## Client-Side Reflex Callbacks
StimulusReflex gives you the ability to inject custom Javascript at four 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. **`after`** - after both `success` and `error`
{% hint style="info" %}
**Using lifecycle callback methods is not a requirement.**
Think of them as power tools that can help you build more sophisticated results. 👷
{% endhint %}
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 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 can define up to four generic lifecycle callback methods. These methods fire for every Reflex action handled by the controller.
1. `beforeReflex`
2. `reflexSuccess`
3. `reflexError`
4. `afterReflex`
{% code title="templates/show\.html" %}
```markup
```
{% endcode %}
{% code title="javascript/controllers/example\_controller.js" %}
```javascript
import { Controller } from 'stimulus'
import StimulusReflex from 'stimulus_reflex'
export default class extends Controller {
connect () {
StimulusReflex.register(this)
}
beforeReflex(anchorElement) {
const { reflex } = anchorElement.dataset
if (reflex.match(/update$/)) anchorElement.innerText = 'Updating...'
if (reflex.match(/delete$/)) anchorElement.innerText = 'Deleting...'
}
}
```
{% endcode %}
In this example, we update each anchor's text before invoking the server side Reflex.
### Custom Lifecycle Methods
StimulusReflex controllers can define up to four custom lifecycle callback methods for **each** Reflex. These methods use a naming convention **based on the name of the Reflex**. For example, the Reflex `ExampleReflex#update` will cause StimulusReflex to check for the existence of the following lifecycle callback methods:
1. `beforeUpdate`
2. `updateSuccess`
3. `updateError`
4. `afterUpdate`
{% code title="templates/show\.html" %}
```markup
```
{% endcode %}
{% code title="javascript/controllers/example\_controller.js" %}
```javascript
import { Controller } from 'stimulus'
import StimulusReflex from 'stimulus_reflex'
export default class extends Controller {
connect () {
StimulusReflex.register(this)
}
beforeUpdate(anchorElement) {
anchorElement.innerText = 'Updating...'
}
beforeDelete(anchorElement) {
anchorElement.innerText = 'Deleting...'
}
}
```
{% endcode %}
Adapting the Generic example, we've refactored our controller to capture the `before` callback events for each anchor individually.
{% hint style="info" %}
**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**.
{% endhint %}
### 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. `afterDoStuff`
#### Method Signatures
Both generic and custom lifecycle callback methods share the same arguments:
* `beforeReflex(element, reflex)`
* `reflexSuccess(element, reflex)`
* `reflexError(element, reflex, error)`
* `afterReflex(element, reflex, error)`
**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** - the error message if an error occurred, otherwise `null`
### 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:after`
#### Event Metadata
When an event is captured, you can obtain all of the data required to respond to a Reflex action:
```javascript
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.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.
{% hint style="info" %}
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.
{% endhint %}
### Promises
Are you a hardcore Javascript developer? Then you'll be pleased to know that in addition to lifecycle methods and events, StimulusReflex allows you to write promise resolver functions:
```javascript
this.stimulate('MyReflex#action')
.then(() => this.doSomething())
.catch(() => this.handleError())
```
You can get a sense of the possibilities:
```javascript
this.stimulate('MyReflex#example')
.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
})
```