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Backbone.js previous Model

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  • Last Updated : 13 Jun, 2022
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The Backbone.js previous model is used to get the previous value of the changed attributes, while the change event occurs in a given model. It will return the actual attribute of the model.

Syntax:

Backbone.Model.previous(attribute);

Parameter Value: It accepts one parameter, which is described below:

  • attribute: This parameter specifies the model’s property.

Example 1: In this example, we are creating a model named orders and changing orderid. After that, we are applying the previous model to return the previous value.

HTML




<!DOCTYPE html>
<html>
<head>
    <script src=
            type="text/javascript">
    </script>
    <script src=
            type="text/javascript">
    </script>
    <script src=
            type="text/javascript">
    </script>
</head>
  
<body>
    <script type="text/javascript">
    var orders = new Backbone.Model({
        orderid: 180,
        ordername: 'clothes',
        address: 'guntur'
    });
    orders.set('orderid', 21);
    document.write(JSON.stringify(orders.previous('orderid')));
    </script>
</body>
</html>


Output:

180

Example 2: In this example, the item value is changed & accordingly displays both the values i.e. the last value & the changed value.

HTML




<!DOCTYPE html>
<html>
  
<head>
    <script src=
            type="text/javascript">
    </script>
    <script src=
            type="text/javascript">
    </script>
    <script src=
            type="text/javascript">
    </script>
</head>
  
<body>
    <script type="text/javascript">
        var Fruit = new Backbone.Model({
            item: "Grape",
            taste: "sweet."
        });
        Fruit.set('item', 'GRAPES');
        document.write("Item's value after set: ", 
            JSON.stringify(Fruit.changedAttributes()));
        document.write("<br>");
        document.write("Item's Last value: ",
            Fruit.previous('item'));
    </script>
</body>
</html>


Output:

Item's value after set: {"item":"GRAPES"}
Item's Last value: Grape

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


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