# ember/avoid-leaking-state-in-ember-objects

💼 This rule is enabled in the ✅ `recommended` [config](https://github.com/ember-cli/eslint-plugin-ember#-configurations).

<!-- end auto-generated rule header -->

Don't use arrays and objects as default properties in classic classes or mixins. In native classes, it is safe to assign objects to fields.

## Examples

Examples of **incorrect** code for this rule:

```js
export default Foo.extend({
  items: [],

  actions: {
    addItem(item) {
      this.items.pushObject(item);
    },
  },
});
```

```js
import Mixin from '@ember/object/mixin';

export default Mixin.create({
  items: [],
});
```

Examples of **correct** code for this rule:

```js
export default Foo.extend({
  init(...args) {
    this._super(...args);

    this.items = this.items || [];
  },

  actions: {
    addItem(item) {
      this.items.pushObject(item);
    },
  },
});
```

```js
import Component from '@glimmer/component';
import { action } from '@ember/object';

export default class FooComponent extends Component {
  items = [];

  @action
  addItem(item) {
    this.items = [...this.items, item];
  }
}
```

## Configuration

If you have custom properties where you know that the shared state won't be a problem (for example, read-only configuration values), you can configure this rule to ignore them by passing the property names to the rule as follows. Note that this rule will always automatically ignore known-safe Ember properties such as `actions`.

```js
module.exports = {
  rules: {
    'ember/avoid-leaking-state-in-ember-objects': [
      'error',
      ['array', 'of', 'ignored', 'properties'],
    ],
  },
};
```

## References

- [Dockyard blog](https://dockyard.com/blog/2015/09/18/ember-best-practices-avoid-leaking-state-into-factories)
- [Ember native classes guides](https://guides.emberjs.com/release/upgrading/current-edition/native-classes/)
- [ember-native-class-codemod](https://github.com/ember-codemods/ember-native-class-codemod)