EmberJS- Computed Properties

Computed Properties

A computed property allows declaring functions as properties. The Ember.js automatically calls the computed properties when needed and combines one or more properties in one variable.

App.Car = Ember.Object.extend({
   CarName: null,
   CarModel: null,

   fullDetails: function() {
      return this.get('CarName') + ' ' + this.get('CarModel');
   }.property('CarName', 'CarModel')
});

In the above code, fullDetails is a computed property which calls property() method to render the two values i.e. CarName and CarModel. Whenever fullDetails gets called, it returns CarName and CarModel.

Example

<!DOCTYPE html>
<html>
   <head>
      <title>Emberjs Computed Properties</title>
      <!-- CDN's-->
      <script src="https://cdnjs.cloudflare.com/ajax/libs/handlebars.js/3.0.1/handlebars.min.js"></script>
      <script src="https://code.jquery.com/jquery-2.1.3.min.js"></script>
      <script src="https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.10.0/ember.min.js"></script>
      <script src="https://builds.emberjs.com/tags/v1.10.0-beta.3/ember-template-compiler.js"></script>
      <script src="https://builds.emberjs.com/release/ember.debug.js"></script>
      <script src="https://builds.emberjs.com/beta/ember-data.js"></script>
   </head>
   <body>
      <script type="text/javascript">
         App = Ember.Application.create();
         App.Car = Ember.Object.extend({
            //the values for below Variables to be supplied by `create` method
            CarName: null,
            CarModel: null,
            fullDetails: function(){
               //returns values to the computed property function fullDetails
               return ' Car Name: '+this.get('CarName') + ' Car Model: ' + this.get('CarModel');
               //property() method combines the variables of the Car
            }.property('CarName', 'CarModel')
         });

         var car_obj = App.Car.create({
            //initializing the values of Car variables
            CarName: "Alto",
            CarModel: "800",
         });
         //Displaying the Car information
         document.write("Details of the car: <br>");
         document.write(car_obj.get('fullDetails'));
      </script>
   </body>
</html>

Output

Let's carry out the following steps to see how above code works −

Save above code in computed_prop.htm file
Open this HTML file in a browser.

The following table lists down the properties of the computed property −

S.N.	Properties & Description
1	Alternate Invocation It passes one or more values to the computed property without using the property() method.
2	Chaining Computed Properties The chaining computed propertiy is used to aggregate with one or more predefined computed properties.
3	Dynamic Updating Dynamically updates the computed property when they are called.
4	Setting Computed Properties Set up the computed properties by using the setter and getter.