Ember-diff-attrs NPM

ember-diff-attrs

This addon was spun out of a discussion on emberjs/rfcs#191 Deprecate component lifecycle hook arguments.

ember-diff-attrs provides a dry way to track attribute changes using a component's didReceiveAttrs lifecycle hook.

PRs, RFCs and comments are welcome!

ember-did-change-attrs

@GavinJoyce and I (mostly Gavin) created an alternative version of this addon that offers a slightly cleaner API using a mixin instead of a decorator.

See: ember-did-change-attrs

Usage

Shorthand usage

import diffAttrs from 'ember-diff-attrs';

export default Ember.Component.extend({
  didReceiveAttrs: diffAttrs('email', 'isAdmin', function(changedAttrs, ...args) {
    this._super(...args);

    if(changedAttrs && changedAttrs.email) {
      let oldEmail = changedAttrs.email[0],
          newEmail = changedAttrs.email[1];
      // Do stuff
    }
  })
});

Some quick notes:

The function hook provided to diffAttrs will always be called, even when a tracked attr is not changed.
changedAttrs will be null on the first call.

Extended usage

import diffAttrs from 'ember-diff-attrs';

export default Ember.Component.extend({
  didReceiveAttrs: diffAttrs({
    keys: ['user', 'isAdmin'],
    isEqual(key, a, b) {
      if (key === 'user') {
        return (a && b) ? a.id === b.id : a === b;
      }
      return a === b;
    },
    hook(changedAttrs, ...args) {
      this._super(...args);

      if(changedAttrs && changedAttrs.user) {
        let oldUser = changedAttrs.user[0],
            newUser = changedAttrs.user[1];
        // Do stuff
      }
    }
  })
});

Design thoughts / rationales.

changedAttrs null on init -- It seems likely that some users will want an alternate behavior for init vs update. There is no loss of functionality by having changedAttrs null on init and it's easy to explain, nothing has actually changed yet.
changedAttrs structure -- I followed the precedence started by ember-data (model.changedAttributes()).

Outstanding Questions

Changed attrs format

I followed ember-data's precedence for representing old and new values (model.changedAttributes()). This format has always felt odd to me. I'm more than happy to discuss changing this.

didUpdateAttrs

Since this addon is implemented as a macro, it cannot easily utilize a component's init call to setup. Because of this, we are unable to determine what has changed the first time didUpdateAttrs is called.