Class Ember.ComputedProperty

Access the value of the function backing the computed property. If this property has already been cached, return the cached result. Otherwise, call the function passing the property name as an argument.

var Person = Ember.Object.extend({
  fullName: function(keyName) {
    // the keyName parameter is 'fullName' in this case.
    return this.get('firstName') + ' ' + this.get('lastName');
  }.property('firstName', 'lastName')
});


var tom = Person.create({
  firstName: 'Tom',
  lastName: 'Dale'
});

tom.get('fullName') // 'Tom Dale'

In some cases, you may want to annotate computed properties with additional metadata about how they function or what values they operate on. For example, computed property functions may close over variables that are then no longer available for introspection.

You can pass a hash of these values to a computed property like this:

person: function() {
  var personId = this.get('personId');
  return App.Person.create({ id: personId });
}.property().meta({ type: App.Person })

The hash that you pass to the meta() function will be saved on the computed property descriptor under the _meta key. Ember runtime exposes a public API for retrieving these values from classes, via the metaForProperty() function.

Sets the dependent keys on this computed property. Pass any number of arguments containing key paths that this computed property depends on.

var President = Ember.Object.extend({
  fullName: computed(function() {
    return this.get('firstName') + ' ' + this.get('lastName');

    // Tell Ember that this computed property depends on firstName
    // and lastName
  }).property('firstName', 'lastName')
});

var president = President.create({
  firstName: 'Barack',
  lastName: 'Obama'
});

president.get('fullName'); // 'Barack Obama'

Call on a computed property to set it into read-only mode. When in this mode the computed property will throw an error when set.

var Person = Ember.Object.extend({
  guid: function() {
    return 'guid-guid-guid';
  }.property().readOnly()
});

var person = Person.create();

person.set('guid', 'new-guid'); // will throw an exception

Set the value of a computed property. If the function that backs your computed property does not accept arguments then the default action for setting would be to define the property on the current object, and set the value of the property to the value being set.

Generally speaking if you intend for your computed property to be set your backing function should accept either two or three arguments.

var Person = Ember.Object.extend({
  // these will be supplied by `create`
  firstName: null,
  lastName: null,

  fullName: function(key, value, oldValue) {
    // getter
    if (arguments.length === 1) {
      var firstName = this.get('firstName');
      var lastName = this.get('lastName');

      return firstName + ' ' + lastName;

    // setter
    } else {
      var name = value.split(' ');

      this.set('firstName', name[0]);
      this.set('lastName', name[1]);

      return value;
    }
  }.property('firstName', 'lastName')
});

var person = Person.create();

person.set('fullName', 'Peter Wagenet');
person.get('firstName'); // 'Peter'
person.get('lastName');  // 'Wagenet'

Call on a computed property to set it into non-cached mode. When in this mode the computed property will not automatically cache the return value.

var outsideService = Ember.Object.extend({
  value: function() {
    return OutsideService.getValue();
  }.property().volatile()
}).create();