Backbone.js collection.length()

Length is a property of the collection. It is used to count the number of models that the collection contains.

Syntax:

Let's take an example.

See this example:

<!DOCTYPE html>
   <head>
      <title>Length Collection Example</title>
         <script src="https://code.jquery.com/jquery-2.1.3.min.js" type="text/javascript"></script>
         <script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.2/underscore-min.js" type="text/javascript"></script>
         <script src="https://cdnjs.cloudflare.com/ajax/libs/backbone.js/1.1.2/backbone-min.js" type="text/javascript"></script>
   </head>
   <body>
      <script type="text/javascript">
    //'Cities' is a model and contains defualt value for the model
         var Cities = Backbone.Model.extend({
            defaults: {
               city: "Hyderabad"
            }
         });

         //'CityCollection' is an instance of the collection
         var CityCollection = Backbone.Collection.extend({
            model: Cities  //model 'Cities' is specified by using model property
         });

         //The add() method adds the models 'city1', 'city2' and 'city3' to the collection instance 'mycollection'
         var city1 = new Cities({city: "Banglore"});
         var city2 = new Cities({city: "Delhi"});
         var city3 = new Cities({city: "Mumbai"});
         var mycollection = new CityCollection();
         mycollection.add([city1,city2,city3]);
         document.write('Number of models in collection : ' + mycollection.length);
      </script>
   </body>
</html>

Test it Now

Output:

Save the above code in length.html file and open this file in a new browser.