Subclassing widget is most important for Odoo.With the help of subclassing Widget() we can change the standard manner with the extend() method, and provides a number of abstract properties and concrete methods .Subclassing Widget looks like this:

var MyWidget = Widget.extend({
    // QWeb template to use when rendering the object
    template: "MyQWebTemplate",
    events: {
        // events binding example
        'click .my-button': 'handle_click',
    },

    init: function(parent) {
        this._super(parent);
        // insert code to execute before rendering, for object
        // initialization
    },
    start: function() {
        var sup = this._super();
        // post-rendering initialization code, at this point

        // allows multiplexing deferred objects
        return $.when(
            // propagate asynchronous signal from parent class
            sup,
            // return own's asynchronous signal
            this.rpc(/*  */))
    }
});

Note-you will have to first call render() on the widget, then insert it into your Subclassing Widget and start it.