Backbone.js previous Model

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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= 
"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"> 
    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:

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= 
"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"> 
        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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