Not recognizing the responsiveFormula

Code:

    plugins: 'responsive',
    responsiveFormulas: {
        phone: function (context) {
            return Ext.os.deviceType == 'Phone';
        },
        tablet: function (context) {
            return Ext.os.deviceType == 'Tablet';
        },
        desktop: function (context) {
            return Ext.os.deviceType == 'Desktop';
        }
    },
    responsiveConfig: {
        desktop: {
            width: 300
        }
    },

I have this configuration on Panel. It throws desktop is not defined error. I am not being able to create new formula. Anyone knows how to do it?



Not recognizing the responsiveFormula