This method is used to set a format for displaying the values.
The diagram on the left is using the default d=>d
and the diagram on the right is using a custom comma formatter.
Modified http://vizjs.org/viz.v1.1.0.min.js to a secure url
https://d3js.org/d3.v4.min.js
https://vizjs.org/viz.v1.1.0.min.js