Backwards compatibility for ES classes in Ember

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101.0.56 years ago6 years agoMinified + gzip package size for ember-legacy-class-shim in KB


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This addon adds a shim which reopens EmberObject and redefines .extend. This allows older versions of Ember to use ES Classes with some restrictions.

Why is this needed?

The reason legacy versions of Ember need this transform lies, at its core, in the double extend which was used for the longest time to inject services and other things. This double extend ends up creating a new class altogether which, due to the way classes are handled internally in Ember, never calls super.
This means that when we define a class using class it's constructor never gets run. A side-effect of this is that class fields, which are assigned in the constructor, do not get assigned. This substantially reduces the usefulness of class syntax and decorators since they rely on class fields working as expected.

What does it fix?

This fixes the double extend problem only. Actually fixing .extend requires changes to CoreObject directly and won't be fixed until later versions of Ember. Once you start using native class syntax, you can't go back.


  • git clone <repository-url> this repository
  • cd ember-legacy-class-shim
  • npm install


Running Tests

  • npm test (Runs ember try:each to test your addon against multiple Ember versions)
  • ember test
  • ember test --server


  • ember build

For more information on using ember-cli, visit https://ember-cli.com/.