自定义 BackboneJS 事件（增量和减量）不起作用

Question

I am having a counter(No. of products) that I want to manipulate using backboneJS custom events. If I click Add Product then No. of products should increase by and if I click Remove Product then No. of products should decrease by one. Demo here The problem is, value of counter is not getting updated when i click buttons. here is code snippet

var Counter = Backbone.Model.extend({
 defaults: { value: 10 },

 // model methods
 increment: function() { 
   this.set({value: this.get('value')+1});
 },
 decrement: function() {
   this.set({value: this.get('value')-1});
 }
});
var cnt = new Counter();
// ------- view ------- 
var AppView = Backbone.View.extend({
 el:'#no_of_products',
 render: function() {
   this.$el.html(this.model.get('value'));
 },

 events:{
   'click .add-one': 'addOne',
   'click .minus-one': 'minusOne'
 },
 initialize: function() {
   this.model.on('change', this.render, this);
   this.render();
 },

 // view methods
 addOne: function() {
   this.model.increment();
 },
 minusOne: function() {
   this.model.decrement();
 }
});
var view = new AppView({ model: cnt });

And html code is:

<div id="product_details">
<h1>No of Products:<span id="no_of_products">0</span></h1>
<table>
  <tr>
    <td>
      Add Product
    </td>
    <td>
     : <button class="add-one">+1</button>
    </td>
  </tr>
  <tr>
    <td>
      Remove Product
    </td>
    <td>
      : <button class="minus-one">- 1</button>
    </td>
  </tr>
</div>

Answer 1

Here's a working example: https://codepen.io/tilwinjoy/pen/OJPyNbR?page=1&

There was few issues:

1. The elements you are trying to bind events to has to be inside the view. In your case view element was only a <span> and everything was outside.
2. Backbone doesn't have two way binding (though there are extensions that can bring such ability) so after updating the model you have to re-render the view yourself

Answer 2

The following code will fix the issue with a test case, however, it won't work if you run it in the browser, but who cares when this helps to clear the test;) Just modified the code to clear the test case.

var Counter = Backbone.Model.extend({
  defaults: { no_of_products: 10 }
});
var cnt = new Counter();
// ------- view -------
var AppView = Backbone.View.extend({
  el:'#product_details',
  render: function() { this.$('#no_of_products').html(this.model.get('no_of_products'));
  },

  events:{
    'click .add-one': 'addOne',
    'click .minus-one': 'minusOne'
  },
  initialize: function() {
    this.model.on('change', this.render, this);
    this.render();
  },

  // view methods
  addOne: function() {
    this.model.set({no_of_products: this.model.get('no_of_products')+1});
    this.render();
  },
  minusOne: function() {
    this.model.set({no_of_products: this.model.get('no_of_products')-1});
    this.render();
  }
});
var view = new AppView({ model: cnt });