dry-observer

A utility to setup DRY event listeners.

npm install dry-observer
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dry-observer

Dryly bind and unbind event listeners and encourage consistent, pattern-based naming of handlers/callbacks.

Build Status

# Observe a Model by passing a hash…
@observe model,
  'song:change'   : @onSongChange
  'volume:change' : @onVolumeChange
  'focus'         : @onFocus

# …or a String or Array.
# Observation will camelCase and prefix your events.
@observe model, 'song:change volume:change focus'

# Stop observing and dereference your model…
@stopObserving model

# …or stop observing /everything/
@stopObserving()

# …or remove a specific handler and cleanup.
@removeObserver model, 'song:change', @onSongChange

Problem

If you're working a lot with Backbone (or other EventEmitter-based APIs), you may have written or reviewed code that's similar to this:

# app/assets/javascripts/views/tasks/detail.js.coffee
class TaskDetail extends Backbone.View
  initialize: ->
    @model.on 'change:closed',    @handleUpdatable
    @model.on 'focus',            @handleFocus
    @model.on 'resetAssignee',    @resetAssignee
    @model.on 'positionUpdated',  @updatePosition
    # etc

  remove: ->
    @model.off 'change:closed',   @handleUpdatable
    @model.off 'resetAssignee',   @resetAssignee
    @model.off 'positionUpdated', @updatePosition
    super

There a number of problems with this code:

  • Events aren't named or formatted uniformly.
  • Handlers aren't consistently named, and may or may not rely on arguments passed by #trigger or #emit.
  • Repetitive calls to #on and #off on different objects adds unDRY cruft to your codebase and…
  • It's easy to forget to bind or unbind events, or update the names of your handlers as you go.

Solution

Observation helps you solve each of these problems by allowing you to centralize both binding and unbinding to events, and by encouraging consistent handler naming.

# app/assets/javascripts/views/tasks/detail.js.coffee
#
class TaskDetail extends App.View
  initialize: ->
    # `#observe` automatically calls `#on` for you, optionally intuiting
    # proper handler names and checking to ensure they exist.
    #
    @observe @model, 'change:closed focus position:updated assignee:reset'

To fully leverage the usefullness of Observation, create a base subclass of Backbone.View you can use to ensure that event listeners always get cleaned up upon view removal.

# app/assets/javascripts/views/base.js.coffee
#
class App.View extends Backbone.View
  # …
  remove: ->
    # Removes all listeners and references to objects observed by a
    # call to `#observe`
    @stopObserving()
    super

# Add Observers to our View base class.
_.extend App.View::, Observers

# app/assets/javascripts/controllers/task_controller.js.coffee
#
# Elsewhere in your code, you decide to remove your TaskDetail view,
# calling the standard Backbone.View#remove() method, perhaps along
# with navigating elsewhere in your app.

detailView.remove()

Contributions

Patches and bug reports are welcome. Just send a pull request or file an issue. Project Changelog.

License

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