I'm building my first line graph in d3:

<http://jsfiddle.net/j94RZ/>

I want to know how to utilize either the scale or axis allow me to draw a grid (of, presumably rectangles) where I can set a different background colour for each of the section of the grid...so I can alternate colours for each cell of the grid. I want the grid to be drawn and be constrained by the axes of my graph and then also adapt if the spacing of the axes ticks change (i.e. the axes changes like this: <http://bl.ocks.org/mbostock/1667367>). So if my graph has an x axis with 4 ticks and a y axis of 7 ticks then my graph will have a background grid that's 7 blocks high and 4 blocks wide.

I've been playing with the idea of using a range which starts at zero and ends at the full width of the graph but I don't know what value I can use for the step. Is there any way to sort of query the axis and return how many ticks there are? 

```
var gridRange = d3.range(0, width, step?); 

```