D3 working days visualizes a full year of daily activity, distinguishing workdays from bank holidays and personal holidays. The SVG animation displays each month as a column of color-coded cells, with days arranged by weekday position and rows wrapping by week. Using D3.js v4 and Moment.js, the code generates all 366 days of 2016, checks each date against two holiday dictionaries, and calculates layout positions for the rectangles. The final render scales to the browser viewport, with the calendar grid revealing the distribution of time off across the year.