backbone.js - Undefined is not a function -

i've started learning backbone.js , tried write first app collections. here code:

console.clear(); (function($){     window.app = {        models : {},       collections : {},       views : {}     };       //a single estimate    app.models.estimate = backbone.model.extend({});     // multiple esitmates    app.collections.estimates  = backbone.collection.extend({         model : app.collections.estimate      });      app.views.estimates = backbone.view.extend({       tagname: 'ul',         render : function(){        this.collection.each(this.addto,this);     },       addto:function(estimate){           var dir = app.views.estimate({model:estimate}).render();          this.$el.append(dir.el);        }         });      app.views.estimate  = backbone.view.extend({       tagname: 'li',         render :function(){           this.$el.html(this.model.get('title'));          return this;       }      });       var json = [{title:'abhiram', estimate:8}];    var estimates = new app.collections.estimates(json);     console.log(estimates);     var tasksview = new app.views.estimates({collection:estimates});   // var = tasksview.render().el;    //console.log(a);  })($j||jquery); 

i've 3 included :

jquery first, underscore next , backbone. keep getting "undefined not function".please let me know if doing wrong.

thanks!

are sure want assign collection app.collections.estimate model self?

// multiple esitmates app.collections.estimates  = backbone.collection.extend({     model : app.collections.estimate });