In this chapter, we learned how to highlight elements when a user moves the pointer over them, making it easier for the user to spot the elements under the cursor and give hints of which elements can provide additional interactions. We created a reusable tooltip component that can be configured and used in other charts.
We also learned how to use the built-in brush component to create a control in order to select intervals, and used this control to allow the user to select a time interval in an area chart. We used the brush area to further annotate the chart with useful information about variations and the edges of the selected time interval.
In the next chapter, we will learn how to add interaction between chart components and how to integrate D3 and Backbone to create complex applications.