Allow passing of context to mixin components about d3.chart

[jugglinmike]

Hey @fscofield, thanks for taking the time to write such a detailed report!

How about adding an initialize method to your original "overlay" chart? You
can then explicitly pass the "overlay" exactly what it needs:

this.mixin("overlay", this.base.append("g"), {
  xScale: this.x,
  yScale: this.y,
  // If these properties are dynamic, you'll want to define getter
  // functions and bind them to the chart
  width: this.w - this.margins.left,
  height: this.h - this.margins.bottom
});

If you want to go brute force, you could just initialize the overlay chart with
a reference to the parent chart:

this.mixin("overlay", this.base.append("g"), { parent: this });

This second approach is functionally equivalent to the solution that you've
suggested. I have been hesitant to facilitate this at an API level because I
think it will encourage people to create less-reusable charts. When authoring a
chart, you want the requirements to be as obvious as possible so that if anyone
else wants to use it, they have a clear contract to fulfill.

Will this work for your use case?

[fscofield]

Mike,

Your solution works great, although as you point out it allows for the creation of graphs that rely on a parent. This works fine for what we're working on however.

Thanks!

[jugglinmike]

I'm glad that will work for you, Forrest!

Regarding the issue of dependency on the parent: Unless I'm mistaken, doesn't your proposal also produce graphs that rely on their parent? It seems like this is actually a requirement of the use case. Don't mean to beat a dead horse, but I want to make sure I understand your proposal before I forget about all this :)

[fscofield]

Yep it does, even though it sort of goes against the mantra of creating fully reusable charts. After reading your suggestion I don't think there's any need to change d3.chart's functionality.

I've been implementing d3.charts for a few weeks now -- I've been really impressed at it's simplicity so far. Thanks to you and Irene for all the hard work!