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Backbone.js hasChanged Model

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  • Last Updated : 20 Jun, 2022

In this article, we will see the Backbone.js hasChanged() model. The hasChanged() model checks if the model is changed or not, i.e. it will return a boolean value as true if the value is changed, otherwise returns a false value, since its last set, in order to set that value for an attribute in the model.

Syntax:

Backbone.Model.hasChanged(attribute);

Parameter Value:

  • attribute: This parameter specifies the property of the model.

Example 1: In this example, we will update the value of a model and check using the hasChanged() model.

HTML




<!DOCTYPE html>
<html>
  
<head>
            type="text/javascript">
      </script>
    <script src=
            type="text/javascript">
      </script>
    <script src=
            type="text/javascript">
      </script>    
</head>
  
<body>
    <script type="text/javascript">
      var Books = Backbone.Model.extend();
      var book = new Books({
          book_name: "css"
      });
      document.write('Actual Values: ' 
                     + JSON.stringify(book));
      document.write("<br>");
      document.write('Actual Value Changed ?: ' 
                     + book.hasChanged());
      book.set('book_name', 'php');
      document.write("<br>");
      document.write("<br>");
      document.write('Changed Values: ' 
                     + JSON.stringify(book));
      document.write("<br>");
      document.write('Actual Value Changed ?: ' 
                     + book.hasChanged());
    </script>
</body>
</html>


Output:

Actual Values: {"book_name":"css"}
Actual Value Changed ?: false

Changed Values: {"book_name":"php"}
Actual Value Changed ?: true

Example 2: In this example, we will update the value of an empty model and check using the hasChanged() model.

HTML




<!DOCTYPE html>
<html>
  
<head>
            type="text/javascript">
      </script>
    <script src=
            type="text/javascript">
      </script>
    <script src=
            type="text/javascript">
    </script>
</head>
  
<body>
    <script type="text/javascript">
      var Books = Backbone.Model.extend();
      var book = new Books({});
      document.write('Actual Values: ' 
                     + JSON.stringify(book));
      document.write("<br>");
      document.write('Actual Value Changed ?: ' 
                     + book.hasChanged());
      book.set('book_name', 'php');
      document.write("<br>");
      document.write("<br>");
      document.write('Changed Values: ' 
                     + JSON.stringify(book));
      document.write("<br>");
      document.write('Actual Value Changed ?: ' 
                     + book.hasChanged());
    </script>
</body>
</html>


Output:

Actual Values: {}
Actual Value Changed ?: false

Changed Values: {"book_name":"php"}
Actual Value Changed ?: true

Reference: https://backbonejs.org/#Model-hasChanged


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