Simple finite state machine (FSM) implementation

fsm.js

"use strict";

function FSM(states, start, accepting) {

  function _accepts(state, word) {
    if (word === "") {
      return accepting.indexOf(state) !== -1;
    }

    return _accepts(states[state][word[0]], word.slice(1));
  }

  return {
    accepts(word) {
      return _accepts(start, word);
    }
  };
}


// machine accepting binary strings (left to right) divisible by five
const states = {
  "%0": {
    "0": "%0",
    "1": "%1"
  },
  "%1": {
    "0": "%2",
    "1": "%3"
  },
  "%2": {
    "0": "%4",
    "1": "%0"
  },
  "%3": {
    "0": "%1",
    "1": "%2"
  },
  "%4": {
    "0": "%3",
    "1": "%4"
  }
};

const fsm = FSM(states, "%0", ["%0"]);

Array(11).fill(0).map((c, i) => {
  return i.toString(2);
}).forEach(c => {
  console.log(c, fsm.accepts(c));
});