1) How does one cell send messages to another. I suppose this is left to the application?

There are several ways to do this https://github.com/intercellular/tutorial#3-inter-cellular-c...

I'm sure there are other ways of doing this in more creative ways, which was my intention when I was designing this to be as simple and modular as possible.

Another thing is, I say Cell has a decentralized architecture, but that doesn't mean it only lets you build apps that way. The point is you can construct these decentralized cells in any way you desire to build apps. So you could build a perfectly centralized architecture with Cell as well.

2) How do you test code written in Cell.js? It appears to me that this is going to be hard to do?

What I think is really cool about this approach is you are effectively expressing an entire app as a piece of data https://github.com/intercellular/cell#3-app-as-data I think this concept needs some time to sink it at first, but once you get it, it opens door to a lot of creative ways of structuring your app.

For starters, any Javascript object can be composed/manipulated/constructed with a function. And since you can express not just data but also the app logic itself as data, you can do the same with stateless functions.

So YES, you can unit test your Cell apps. In fact it's easier than any other existing frameworks since the entire app is built with functional programming (no stateful class objects). You can write a whole bunch of functions to construct/manipulate these "Genotype" objects and unit test those functions to make sure they behave correctly. Hope this makes sense.

3) Is it intended that the entire webapp code be a single JS file? I guess one would need a server side build step to "assemble" multiple Cell.js components into a single one?

Nope, the only reason I packaged them as a single file at https://play.celljs.org was just to make it easier to understand as a demo (because splitting out into multiple files makes you jump back and forth and is not ideal when you're just trying to have a quick overview of the app structure).

But the beauty of this approach is, at the end of the day, all you need is a JSON-like object that defines the looks and behaviors of your HTML nodes throughout the DOM tree. Which means in real life, you would be splitting these out into as many functions as you want (In fact this is one of the strongest selling points of Cell. you can create as many of these functional components as you want without overhead compared to other class based frameworks) Really at the end of the day all you need is a function that generates the Javascript object structure you need, which means you can map/filter/reduce anything from Model to View to Controller logic.

Here's an example I was working on yesterday https://github.com/intercellular/jsonschema It's a JSON schema validator, still work in progress since I just started it yesterday but you get the point.

Hope this was helpful. Please feel free to ask more questions!