Deprecate Observers

Author: wagenet

text/1115-deprecate-observable.md

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+---
+stage: accepted
+start-date: 2025-06-16T00:00:00.000Z
+release-date:
+release-versions:
+teams: # delete teams that aren't relevant
+  - cli
+  - data
+  - framework
+  - learning
+  - steering
+  - typescript
+prs:
+  accepted: https://github.com/emberjs/rfcs/pull/1115
+project-link:
+---
+
+# Deprecate Observers
+
+## Summary
+
+Deprecate the `Observable` Mixin, `observer` helper, and public observer functionality.
+
+## Motivation
+
+Using observers has been soft-deprecated ever since the introduction of tracking. Removing
+support for them will significantly clean up the code base. (Note that for us to entirely
+remove observer support internally, we will likely need to deprecate other functionality
+in addition to what is include here.)
+
+Additionally, Ember has also not recommended the use of Mixins for a while. Since
+`Observable` uses the Mixin architecture, it will also need to be deprecated for us
+to fully remove Mixins.
+
+## Transition Path
+
+### Observable Mixin
+
+Some of the methods provided by `Observable` are available as standalone methods,
+for these the transition path is straight-forward:
+
+* `get` -> Import from `@ember/object`
+* `getProperties` -> Import from `@ember/object`
+* `set` -> Import from `@ember/object`
+* `setProperties` -> Import from `@ember/object`
+* `notifyPropertyChange` -> Import from `@ember/object`
+
+For sugar helpers they can easily be replaced with a bit more verbosity:
+
+* `incrementProperty`
+    ```js
+    this.count += 1; // Tracking
+    set(this, 'count', get(this, 'count') + 1); // Legacy 
+    ```
+* `decrementProperty`
+    ```js
+    this.count -= 1; // Tracking
+    set(this, 'count', get(this, 'count') - 1); // Legacy 
+    ```
+* `toggleProperty`
+    ```js
+    this.flag = !this.flag; // Tracking
+    set(this, 'flag', !get(this, 'flag')); // Legacy
+    ```
+
+For others, there will no replacement and code that depends on them
+will have to be refactored:
+
+* `addObserver`
+* `removeObserver`
+* `cacheFor`
+
+### Observable Helper
+
+This function does not work with native class syntax and as such, shouldn't be relied upon.
+It will not be replaced.
+
+## Exploration
+
+To validate this deprecation, I've tried removing this functionality in the following PRs:
+* Inline Observable Mixin: https://github.com/emberjs/ember.js/pull/20928
+* Remove `observer` helper: https://github.com/emberjs/ember.js/pull/20935
+* Remove inlined Observable methods: https://github.com/emberjs/ember.js/pull/20929 (Note this PR may change.)
+
+## How We Teach This
+
+We should remove all references to this functionality from the guides.
+
+## Drawbacks
+
+Many users probably rely on this functionality. However, it's almost certainly
+something that we don't want to support long-term.
+
+## Alternatives
+
+* Just inline this functionality so that we can at least get rid of Mixins.
+
+## Unresolved questions
+
+None