Simple finite state machine in JavaScript

Lightweight, standalone. Less than 0.25 kB. • Source, minified, ZIP, Github

If you simply want to make sure that your application is in a valid state, this is the state machine to use.

The code has no license, it's in the public domain. I do however appreciate attribution.

Grab the complete minified code, just 233 bytes:

Demo

Usage

Example borrowed from Jake Gordon. Let's create a state machine with a few states and events.

// Ssm( [initial,] events )
var fsm = Ssm("green", // initial is "none" if first parameter is omitted
	{ // events
		warn:  { from: "green",        to: "yellow" },
		panic: { from: "green yellow", to: "red"    }, // allow to be called from multiple states
		calm:  { from: "red",          to: "yellow" },
		clear: {                       to: "green"  }, // if from state is absent, it can be called from all states
		work:  { from: "green"                      } // if to state is absent, the state won't be changed when the event is called
});

Now we have a simple state machine:

• fsm("warn"), fsm("panic"), fsm("calm"), fsm("clear"), and fsm("work")
  • Transitions the current state to another color.
  • Will throw an exception if the event is not allowed.
• fsm.can("warn"), fsm.can("panic"), fsm.can("calm"), fsm.can("clear"), fsm.can("work")
  • Returns true if the <event> is allowed, else false.
• fsm.current
  • The current state, initially green.
• fsm.events
  • The events object which was used to create the state machine. Note that changing this object will change the machine's behavior.

The methods may be used as follows.

// fsm.current === "green"
if (fsm.can("calm"))
	fsm("calm"); // will never happen - can only calm from red

fsm("panic"); // fsm.current === "red"
fsm("warn");  // throws exception! only allowed from green

Visualize

var fsm = Ssm({ // events

}); Visualize!