Comments on: Finite State Machines in JavaScript

By: The If Works · With a little help from with

The If Works · With a little help from with — Fri, 29 Feb 2008 12:17:48 +0000

[...] I’m going to leave the discussion of what constitutes metaprogramming to another day (read: never), but what I will say is that I’m becoming more interested in DSLs and fluent interfaces. I want the code I write to work at a very high level, where it describes what I’m trying to achieve in terms that anyone else (read: me, six months later) can understand. I particularly like this example of a JavaScript DSL for describing state machines: [...]

By: michael

michael — Sun, 23 Dec 2007 10:02:43 +0000

NicolÃ¡s, thanks for the suggestion. I’ve updated the script accordingly.

By: NicolÃ¡s Sanguinetti

NicolÃ¡s Sanguinetti — Sun, 23 Dec 2007 00:23:39 +0000

Good stuff! I’ll see what I can do for the specs so they look a bit nicer, as the results are pretty rough right now

Regarding the code used to initialize a FSM, most of it is repetitive, so you could extract it into a static method of FSM. And for the declaration of events and states in your machine, you could “yield” the machine description object to a “block”:

var Machine = FSM.build(function(m) {
m.onUnexpectedEvent(…);
m.state(‘start’, …);
…
});

Thing.prototype = new Machine(Thing.prototype);

Then, the FSM.build function would look something like this:

FSM.build = function(block) {
var fsm = new FSM;
block(fsm);
return fsm.buildMachine();
}

(And you can still use with(m) in the “block” if calling methods explicitly bothers you )