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JavaScript: order of defining functions and instance objects

I'm having problems with the order of defining functions and instantiating objects, see the JSFiddle

Right now I'm just playing around with the idea, but I hit this wall and I don't know if there is any simple solution to the problem. Basically I have an object with some methods for another object, but this other object contains references to the first object, so no matter what order I create / define, I get an error because one or the other was not loaded:

  var router = {
    update: function(event, from, to) {
      window.location.hash = "#/" + to;
      $("back-btn").disabled = fsm.can("back");  // *** And here I am referencing fsm
      $("next-btn").disabled = fsm.can("next");
    },
    location: window.location.hash.substring(2),
  }

  var fsm = StateMachine.create({
    initial: "intro",
    events: [

      // Next events and where to route based on our page
      { name: "next", from: "intro", to: "getname" },
      { name: "next", from: "getname", to: "welcome" },
      { name: "next", from: "welcome", to: "why" },

      // We can't go "back" from the initial route
      { name: "back", from: "getname", to: "intro" },
      { name: "back", from: "welcome", to: "getname" },
      { name: "back", from: "why", to: "welcome" } ],

    callbacks: {
      onintro  : router.update, //*** Here I am referencing the router object
      ongetname: router.update,
      onwelcome: router.update,
      onwhy    : router.update 
    }
  });

Thanks for any help.

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4 answers


I had to assign callbacks to the state machine object after the fact, and then defer initialization until my router object was defined:

var fsm = StateMachine.create({

  //*** Here we set defer to true
  initial: { state: "intro", event: "init", defer: true },
  events: [

    // Next events and where to route based on our page
    { name: "next", from: "intro",   to: "getname" },
    { name: "next", from: "getname", to: "welcome" },
    { name: "next", from: "welcome", to: "why" },

    // We can't go "back" from the initial route
    { name: "back", from: "getname", to: "intro" },
    { name: "back", from: "welcome", to: "getname" },
    { name: "back", from: "why",     to: "welcome" } ],
});

window.onload = function() {
  var router = {
    update: function(event, from, to) {
      window.location.hash = "#/" + to;
      $("back-btn").disabled = fsm.cannot("back");
      $("next-btn").disabled = fsm.cannot("next");
    },
    location: window.location.hash.substring(2),
  }

  //*** And now we attach the callbacks since we have created the router object
  fsm.onintro = router.update, fsm.ongetname = router.update,
  fsm.ongetname = router.update, fsm.onwelcome = router.update,
  fsm.onwhy = router.update;

  //*** And call the init event!
  fsm.init();
}


and fiddle

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It looks like the sync issue is happening because one of the callbacks you specify onintro

is supposedly triggered right away. Is it practical to refactor your implementation for a callback onintro

? You could get away with something like this:



var router = {
    update: function(event, from, to) {
        window.location.hash = "#/" + to;
        $("back-btn").disabled = fsm.can("back");
        $("next-btn").disabled = fsm.can("next");
    },
    location: window.location.hash.substring(2),
}

var fsm = StateMachine.create({
    //...

    callbacks: {
        //onintro  : router.update, // Don't call this in the constructor...
        ongetname: router.update,
        onwelcome: router.update,
        onwhy    : router.update 
    }
});

router.update(); // Call it just after construct.
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You can use try/catch

to escape the first undefined:

try {
    $("back-btn").disabled = fsm.can("back");
    $("next-btn").disabled = fsm.can("next");
} catch(e){}

Also, if you test everything in a JSFiddle, this will turn your JS into a function window.onload

. Therefore, when you press buttons, they will try to call fsm.back()

or fsm.next()

where it fsm

was defined within this function window.onload

. Access is not available within these buttons.

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Fixing dependencies can be simple:

var router = {
    update: function(event, from, to) {
        window.location.hash = "#/" + to;
        if(window.fsm) {
            $("back-btn").disabled = fsm.can("back");
            $("next-btn").disabled = fsm.can("next");
        }
    },
    location: window.location.hash.substring(2),
}
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