Bindings

Bindings

Unlike most other frameworks that include some sort of binding implementation, bindings in Ember.js can be used with any object. That said, bindings are most often used within the Ember framework itself, and for most problems Ember app developers face, computed properties are the appropriate solution.

The easiest way to create a two-way binding is to use a computed.alias(), that specifies the path to another object.

husband = Ember.Object.create({
  pets: 0
});

Wife = Ember.Object.extend({
  pets: Ember.computed.alias('husband.pets')
});

wife = Wife.create({
  husband: husband
});

wife.get('pets'); // 0

// Someone gets a pet.
husband.set('pets', 1);
wife.get('pets'); // 1

Note that bindings don't update immediately. Ember waits until all of your application code has finished running before synchronizing changes, so you can change a bound property as many times as you'd like without worrying about the overhead of syncing bindings when values are transient.

One-Way Bindings

A one-way binding only propagates changes in one direction, using computed.oneWay(). Often, one-way bindings are a performance optimization and you can safely use a two-way binding (which are de facto one-way bindings if you only ever change one side). Sometimes one-way bindings are useful to achieve specific behaviour such as a default that is the same as another property but can be overridden (e.g. a shipping address that starts the same as a billing address but can later be changed)

user = Ember.Object.create({
  fullName: 'Kara Gates'
});

UserComponent = Ember.Component.extend({
  userName: Ember.computed.oneWay('user.fullName')
});

userComponent = UserComponent.create({
  user: user
});

// Changing the name of the user object changes
// the value on the view.
user.set('fullName', 'Krang Gates');
// userComponent.userName will become "Krang Gates"

// ...but changes to the view don't make it back to
// the object.
userComponent.set('userName', 'Truckasaurus Gates');
user.get('fullName'); // "Krang Gates"