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ember-classic-decorator

This addon provides a dev-time only class decorator, @classic. This decorator gets removed from production builds, and is entirely for the purpose of helping you navigate the upgrade from Ember's classic class system to native classes in Ember Octane!

Installation

First, install the addon:

ember install ember-classic-decorator

You should also ensure you are using the latest version of the Ember eslint plugin and enable the related eslint rules to gain the full benefits of the decorator:

// .eslintrc.js

  // ...
  rules: {
    'ember/classic-decorator-hooks': 'error',
    'ember/classic-decorator-no-classic-methods': 'error'
  },
  // ...

Why do I need this decorator?

While you can now use native class syntax to extend from any Ember base class, there are still a few differences between classic classes and native classes that can be a little tricky during the conversion:

  • init and constructor are two separate methods that are called at different times. If you convert a class to native class syntax and change its init function to constructor, then it will run before any of its parent classes' init methods. This could leave you in an inconsistent state, and cause subtle bugs.
  • Ember's classic class system uses many static class methods such as create, reopen, and reopenClass, which do not have native class equivalents. Some classes will need to be redesigned to account for this.
  • All Ember classes have a number of methods, like get, set, incrementProperty, and notifyPropertyChange. In the future, most of these methods will not be necessary, and will not exist on future base classes like Glimmer components.
  • Speaking of Glimmer components - if you convert your application to native classes, and then start converting each component to Glimmer components, it could get confusing very quickly. Is this component class a Glimmer component, or a classic component?

@classic provides a hint to you, the developer, that this class uses classic APIs and base classes, and still has some work to do before it can be marked as fully converted to Octane conventions.

What does it do?

When installed, @classic will modify Ember classes to assert if certain APIs are used, and lint against other APIs being used, unless a class is defined with classic class syntax, or decorated with @classic.

The following APIs will throw an error if used in a non-classic class:

  • reopen
  • reopenClass

The following APIs will cause a lint error if used in a non-classic class definition. Since we cannot know everywhere that the class is used, instances of the class may still use these methods and will not cause assertions or lint errors:

  • get
  • set
  • getProperties
  • setProperties
  • getWithDefault
  • incrementProperty
  • decrementProperty
  • toggleProperty
  • addObserver
  • removeObserver
  • notifyPropertyChange

In addition, @classic will prevent users from using constructor in subclasses if the parent class has an init method, to prevent bugs caused by timing issues.

Which classes must be marked as @classic?

Certain classes must always be marked as classic:

  • Classic components
  • Utility classes that extend directly from EmberObject

These must be marked as classic because their APIs are intrinsically tied to the classic class model. To remove the @classic decorator from them, you can:

  • Convert classic components to Glimmer components
  • Rewrite utility classes so they do not extend from EmberObject at all, and only use native class syntax.

Other classes can be converted incrementally to remove classic APIs, including:

  • Routes
  • Services
  • Controllers
  • Class based helpers

How do I refactor and remove @classic?

In order to remove the classic decorator from a class, you must:

  • Remove usage of mixins from the class
  • Remove usage of static class methods on the class, such as reopen and reopenClass
  • Remove usage of classic class methods within the class definition, including:
    • get
    • set
    • getProperties
    • setProperties
    • getWithDefault
    • incrementProperty
    • decrementProperty
    • toggleProperty
    • addObserver
    • removeObserver
    • notifyPropertyChange

Compatibility

  • Ember.js v3.24 or above
  • Ember CLI v3.24 or above
  • Node.js v12 or above

Usage

Apply the @classic decorator to any classes that should use classic APIs.

import EmberObject from '@ember/object';
import classic from 'ember-classic-decorator';

@classic
export default class Foo extends EmberObject {}

Contributing

See the Contributing guide for details.

License

This project is licensed under the MIT License.