ember-computed-change-gate

Observers on Ember.js computed properties are fired if a dependant key changes, regardless of whether the property value changes or not. ember-computed-change-gate only triggers observers when the result of a computed property changes.

Consider the following example:

Ember.Object.extend({
  name: 'Gavin',
  trimmedName: Ember.computed('name'), function() {
    return this.get('name').trim();
  }),
  onTrimmedNameChanged: Ember.observer('trimmedName', function() {
    console.log('trimmedName changed');
  })
});

Every time name changes onTrimmedNameChanged will be run, even if the value of trimmedName doesn't change.

import changeGate from 'ember-computed-change-gate/change-gate';

Ember.Object.extend({
  name: 'Gavin',
  trimmedName: changeGate('name', function(value) {
    return value.trim();
  }),
  onTrimmedNameChanged: Ember.observer('trimmedName', function() {
    console.log('trimmedName changed');
  })
});

Using changeGate will prevent the onTrimmedNameChanged observer from firing unless the value of trimmedName changes. Please see the video below for an example of how I've used this when building Intercom:

Advanced configuration

Since Ember 3.11 extra configuration can be passed to observers to allow them to be configured synchronous or asynchronous. To configure the synchronous state of the observer in changeGate pass a config object as the last param with the sync property set appropriately.

For example:

// synchronous observer
trimmedName: changeGate('name', function(value) {
  return value.trim();
}, { sync: true }),

//asynchronous observer
trimmedName: changeGate('name', function(value) {
  return value.trim();
}, { sync: false }),

See this RFC and blog post for more informationa about async observers.

Watch a screencast showing how this addon was built below

Questions? Ping me @gavinjoyce

Installation

This is an Ember CLI addon, to install:

ember install ember-computed-change-gate

Development Instructions

• git clone this repository
• npm install
• bower install

Linting

• npm run lint:js
• npm run lint:js -- --fix

Running tests

• ember test – Runs the test suite on the current Ember version
• ember test --server – Runs the test suite in "watch mode"
• ember try:each – Runs the test suite against multiple Ember versions

Running the dummy application

• ember serve
• Visit the dummy application at http://localhost:4200.

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

License

This project is licensed under the MIT License.