get last updated brush states issue

Question

I looked every where and I tried several solution but I wasn't able to find something similar to brushend in angular-nvd3 lineWithFocusChart. in fact I'm trying to get the details of the rendered brush extent. I tried

callback : function(chart) {
            chart.focus.dispatch.on('brush', function(e) {
                console.log("hello", e)
            });
        }

But it renders all details and not the last one and when I use 'brushend' i get an error message like if the dispatch is undefined d3.js:492 Uncaught TypeError: Cannot read property 'on' of undefined. Can you please help me :(