Is there a way to pre-set a session variable? about iron-router

[cmather]

Yeah for the first case you can use the onRendered hook. For the second, I'm not sure what HCR means :-).

[tmeasday]

Hot Code Reload.

Hopefully there'll be a way to do this without having to define a controller (I haven't had to explicitly do so so far!).

[tmeasday]

To be clearer: it's a common use case to want to set "view" state for a page in the session.

For example, you might want to Session.set('sidebarOpen', false) every time you browse to a page with a sidebar in it.

If you browse away and then come back, you want the "view" to be reset, so the sidebar to be closed again. However, if there's a HCR, you do not want the view to be reset.

From the router's perspective, it's difficult to tell the difference. I don't think it's impossible though.

[cmather]

Ah yes, Hot Code Reload. I thought about that issue a few times. My inclination is to allow components to handle this as each component will have scoped reactive state. I'm assuming David's implementation allows for HCR, but I haven't confirmed this.

Putting the per page state in the Router would require creating a global reactive dictionary that the router uses. When the page reloads, the route necessarily runs again, creating a new instance of the controller. So the controller instance reactive dictionary would not survive the HCR.

Maybe we should take a closer look at the Component implementation. So far I've only studied the base.js code from a week or so ago. I didn't see a scoped reactive dictionary, but David mentioned it in his talk.

[tmeasday]

Ahh, yes. Well, without knowing details of how UI/Components might work I would hazard a guess that the right thing for the router to do would be register itself for migration and defer to the currently rendered controller to save it's state. Then when a "migrated" startup happens (i.e. after HCR), the first thing the router could do is read that data back out and use it to establish both it's own internal state and that of the rendered controller. After which it would check the URL and make sure everything is kosher with what it expects.

But that's pretty complex and out of scope, I am not suggesting that we do so now!

In the meantime whilst we are stuck using the Session for component state, I'm wondering if the following solution isn't to janky:

// just a little note so we know when we are starting up based on migration
Meteor._reload.onMigrate('iron-router', function() { return [true, Location.path()]; });

// When routing to a controller:

// we don't want to do this when it's the first route we are rendering and we are coming out of HCR
if (! (firstRoute && Meteor._reload.migrationData('iron-router') === Location.path())) {
  controller.beforeRoutingTo();
}
firstRoute = false;

Then I can write something like:

Router.map(function() {
  this.route('foo', {
    beforeRoutingTo: function() {
      Session.set('menuState', 'open');
    }
  });
});

And know for sure that menuState will always be set, but will not be reset when HCR happens.

[cmather]

Assuming this is covered in your PR. Will look today.