CoreObject#mergedProperties

Defines the properties that will be merged from the superclass (instead of overridden).

By default, when you extend an Ember class a property defined in the subclass overrides a property with the same name that is defined in the superclass. However, there are some cases where it is preferable to build up a property's value by merging the superclass property value with the subclass property's value. An example of this in use within Ember is the queryParams property of routes.

Here is some sample code showing the difference between a merged property and a normal one:

App.BarRoute = Ember.Route.extend({
  someNonMergedProperty: {
    nonMerged: 'superclass value of nonMerged'
  },
  queryParams: {
    page: {replace: false},
    limit: {replace: true}
  }
});

App.FooBarRoute = App.BarRoute.extend({
  someNonMergedProperty: {
    completelyNonMerged: 'subclass value of nonMerged'
  },
  queryParams: {
    limit: {replace: false}
  }
});

var fooBarRoute = App.FooBarRoute.create();

fooBarRoute.get('someNonMergedProperty');
// => { completelyNonMerged: 'subclass value of nonMerged' }
//
// Note the entire object, including the nonMerged property of
// the superclass object, has been replaced

fooBarRoute.get('queryParams');
// => {
//   page: {replace: false},
//   limit: {replace: false}
// }
//
// Note the page remains from the superclass, and the
// `limit` property's value of `false` has been merged from
// the subclass.

This behavior is not available during object create calls. It is only available at extend time.

This feature is available for you to use throughout the Ember object model, although typical app developers are likely to use it infrequently. Since it changes expectations about behavior of properties, you should properly document its usage in each individual merged property (to not mislead your users to think they can override the property in a subclass).