to attach or to extend? about d3.chart

[jugglinmike]

If I understand your problem correctly, this sounds like a case for attach. You should be able to re-use the scales; how you do it depends on how you structure your code. Here are two approaches that come to mind:

1. You could define a single chart that initializes the chart you wish to extend, retrieves references to that instance's scales immediately following initialization, and defines the new layer in terms of that reference.
2. You could define two charts. "Chart A" would define the layer you want to add, and it would accept a set of scales as an initialization option. "Chart B" would create one instance of the chart you wish to reuse and one instance of Chart A, passing in the scales as appropriate. Finally, Chart B would use attach to hook up the draw cycles.

The second approach requires more abstraction, but it's also more composable and potentially more flexible for it. Would either work for you?