no-attrs-snapshot.md

ember/no-attrs-snapshot

💼 This rule is enabled in the ✅ recommended config.

Disallow use of attrs snapshot in didReceiveAttrs and didUpdateAttrs.

Do not use the arguments (attrs) that are passed in didReceiveAttrs and didUpdateAttrs. Using the arguments (attrs) in these hooks can result in performance degradation in your application.

Rule Details

In 2.0.0, didReceiveAttrs and didUpdateAttrs hooks were introduced. These hooks are called whenever the references of arguments to a component change. These hooks receive arguments, however one should not use them as they force those objects to reify, which can be very costly when you have a lot of components on the page. These arguments are also purposely undocumented.

If for some reason you need to do a comparison of arguments we suggest that you simply keep a cache on the component.

Examples

Examples of incorrect code for this rule:

import Component from '@ember/component';

export default Component({
  init(...args) {
    this._super(...args);
    this.updated = false;
  },
  didReceiveAttrs(attrs) {
    const { newAttrs, oldAttrs } = attrs;
    if (newAttrs && oldAttrs && newAttrs.value !== oldAttrs.value) {
      this.set('updated', true);
    } else {
      this.set('updated', false);
    }
  }
});

Examples of correct code for this rule:

import Component from '@ember/component';

export default Component({
  init(...args) {
    this._super(...args);
    this._valueCache = this.value;
    this.updated = false;
  },
  didReceiveAttrs() {
    if (this._valueCache === this.value) {
      this.set('updated', false);
    } else {
      this._valueCache = this.value;
      this.set('updated', true);
    }
  }
});

When Not To Use It

You can turn this rule of if you aren't worried about the negative performance impacts of using params in these hooks.

Further Reading

• didReceiveAttrs
• didUpdateAttrs