IPython/html/static/notebook/js/widgets/button.js

require(["notebook/js/widget"], function(){
    
    var ButtonWidgetModel = IPython.WidgetModel.extend({});
    IPython.notebook.widget_manager.register_widget_model('ButtonWidgetModel', ButtonWidgetModel);

    var ButtonView = IPython.WidgetView.extend({
      
        // Called when view is rendered.
        render : function(){
            var that = this;
            this.$el = $("<button />")
                .addClass('btn')
                .click(function() {
                    that.model.set('clicks', that.model.get('clicks') + 1);
                    that.model.update_other_views(that);
                });

            this.update(); // Set defaults.
        },
        
        // Handles: Backend -> Frontend Sync
        //          Frontent -> Frontend Sync
        update : function(){
            var description = this.model.get('description');
            if (description.length==0) {
                this.$el.html(' '); // Preserve button height
            } else {
                this.$el.html(description);
            }
            
            return IPython.WidgetView.prototype.update.call(this);
        },
        
    });

    IPython.notebook.widget_manager.register_widget_view('ButtonView', ButtonView);

});