Carefully Designed Client Side Router for Meteor.

Flow Router is a minimalistic router which only handles routing and subscriptions. You can't have any kind of reactive code inside routes, but there is a reactive API to dynamically change your app based on the state of the router.

• Getting Started
• Routes Definition
• Subscription Management
• Rendering and Layout Management
• Middlewares
• Not Found Routes
• API
• Difference with Iron Router

Add Flow Router to your app:

meteor add meteorhacks:flow-router

Let's write our first route: (Add this file to lib/router.js)

FlowRouter.route('/blog/:postId', {
    subscriptions: function(params) {
        console.log("subscribe and register this subscription as 'myPost'");
        this.register('myPost', Meteor.subscribe('blogPost', params.postId));
    },
    action: function(params) {
        console.log("Yeah! We are on the post:", params.postId);
    }
});

Then visit /blog/my-post-id from the browser or invoke the following command from the browser console:

FlowRouter.go('/blog/my-post-id');

Then you can see some messages printed in the console.

Flow Router routes are very simple and based on the syntax of path-to-regexp which is used in both express and iron-router.

Here's the syntax for a simple route:

FlowRouter.route('/blog/:postId', {
    // an array of middlewares (we'll discuess about this later on)
    middlewares: [],

    // define your subscriptions
    subscriptions: function(params, queryParams) {
       
    },

    // do some action for this route
    action: function(params, queryParams) {
        console.log("Params:", params)
        console.log("Query Params:", queryParams)
    },

    name: "<name for the route>" // optional
});

So, this route will be activated when you visit a url like below:

FlowRouter.go('/blog/my-post?comments=on&color=dark')

After you've visit the route, this will be printed in the console:

Params: {postId: "my-post"}
Query Params: {comments: "on", color: "dark"}

For a single interaction, router only runs once. That means, after you've visit a route, first it will call middlewares, then subscriptions and finally action. After that happens, there is no way any of those methods to be called again for that route visit.

You can define routes anywhere in the client directory. But, we recommend to add it on lib directory. Then fast-render can detect subscriptions and send them for you (we'll talk about this is a moment).

You can also group routes as well. With that, we can group some common functionalities. Here's an example:

var adminRoutes = FlowRouter.group({
  prefix: '/admin',
  subscriptions: function() {
    this.register('adminSettings', Meteor.subscribe('settings', {admin: true}));
  },
  middlewares: [
    function(path, next) {
      console.log('running group middleware');
      next();
    }
  ]
});

// handling /admin route
adminRoutes.route('/', {
  action: function() {
    FlowLayout.render('componentLayout', {content: 'admin'});
  },
  middlewares: [
    function(path, next) {
      console.log('running /admin middleware');
      next();
    }
  ]
});

// handling /admin/posts
adminRoutes.route('/posts', {
  action: function() {
    FlowLayout.render('componentLayout', {content: 'posts'});
  }
});

All of the options for the FlowRouter.group() are optional.

You can even have nested group routes as shown below:

var adminRoutes = FlowRouter.group({
    prefix: "/admin"
});

var superAdminRoutes = FlowRouter.group({
    prefix: "/super"
});

// handling /admin/super/post
superAdminRoutes.route('/post', {
    action: function() {

    }
});

Inside the route, Flow Router only registers subscriptions. It does not wait for the ready message before running the action. This is how to register a subscription.

FlowRouter.route('/blog/:postId', {
    subscriptions: function(params, queryParams) {
        this.register('myPost', Meteor.subscribe('blogPost', params.postId));
    }
});

We can also register global subscriptions like this:

FlowRouter.subscriptions = function() {
  this.register('myCourses', Meteor.subscribe('courses'));
};

All these global subscriptions run on every route. So, make special attention to names when registering subscriptions.

After you've registered your subscriptions, you can reactively check for the status of those subscriptions like this:

Tracker.autorun(function() {
    console.log("Is myPost ready?:", FlowRouter.subsReady("myPost"));
    console.log("Does all subscriptions ready?:", FlowRouter.subsReady());
});

So, you can use FlowRouter.subsReady inside template helpers to show the loading status and act accordingly.

Arunoda has discussed more about Subscription Management in Flow Router in this blog post about Flow Router and Subscription Management.

He's showing how to build an app like this:

Flow Router has built in support for Fast Render.

• meteor add meteorhacks:fast-render
• Put router.js in a shared location. We suggest lib/router.js.

You can selectively exclude Fast Render support by wrapping the subscription registration in an isClient block:

FlowRouter.route('/blog/:postId', {
    subscriptions: function(params, queryParams) {
        // using Fast Render
        this.register('myPost', Meteor.subscribe('blogPost', params.postId));

        // not using Fast Render
        if(Meteor.isClient) {
            this.register('data', Meteor.subscribe('bootstrap-data');
        }
    }
});

You can also use Subs Manager for caching subscriptions on the client. We haven't done anything special to make it work. It should work as it works with other routers.

Flow Router does not handle rendering or layout management. For that, you can use Flow Layout.

Then you can invoke the layout manager inside the action method in the router.

FlowRouter.route('/blog/:postId', {
    action: function(params) {
        FlowLayout.render("mainLayout", {area: "blog"});
    }
});

Sometimes, you need to do invoke some tasks just before entering into the route. That's where middlewares comes in. Here are some of the use cases for middlewares:

• Route Redirecting
• Analytics
• Initialzation tasks

This is how we can implement simple redirection logic with middleware. It will redirect a user to the sign-in page if they are not logged in.

FlowRouter.route('/apps/:appId', {
    middlewares: [requiredLogin],
    subscriptions: function(params) {
        
    },
    action: function(params) {

    }
});

function requiredLogin(path, next) {
  // this works only because the use of Fast Render
  var redirectPath = (!Meteor.userId())? "/sign-in" : null;
  next(redirectPath);
}

You can also write global middlewares like this:

FlowRouter.middleware(trackingMiddleware);

function trackingMiddleware(path, next) {
    console.log("tracking path:", path);
    next();
}

You can configure Not Found routes like this.

FlowRouter.notFound = {
    // Subscriptions registered here don't have Fast Render support.
    subscriptions: function() {
      
    },
    action: function() {
      
    }
};

Flow Router has some utility APIs to help you navigate the router and get information from the router.

Reactive function which you can use to get a param from the URL.

// route def: /apps/:appId
// url: /apps/this-is-my-app

var appId = FlowRouter.getParam("appId");
console.log(appId); // prints "this-is-my-app"

Reactive function which you can use to get a value from the queryString.

// route def: /apps/:appId
// url: /apps/this-is-my-app?show=yes&color=red

var color = FlowRouter.getQueryParam("color");
console.log(color); // prints "red"

Generate a path from a path definition. Both params and queryParams are optional.

var pathDef = "/blog/:cat/:id";
var params = {cat: "meteor", id: "abc"};
var queryParams = {show: "yes", color: "black"};

var path = FlowRouter.path(pathDef, params, queryParams);
console.log(path); // prints "/blog/meteor/abc?show=yes&color=black"

If there are no params or queryParams, this will simply return the pathDef as it is.

You can also use route's name instead of the pathDef. Then, flow router will pick the pathDef from the given route. See following example:

FlowRouter.route("/blog/:cat/:id", {
    name: "blogPostRoute",
    action: function(params) {
        //...
    }
})

var params = {cat: "meteor", id: "abc"};
var queryParams = {show: "yes", color: "black"};

var path = FlowRouter.path("blogPostRoute", params, queryParams);
console.log(path); // prints "/blog/meteor/abc?show=yes&color=black"

This will get the path via FlowRouter.path based on the arguments and re-route to that path.

You can call FlowRouter.go like this as well:

FlowRouter.go("/blog");

This will change the current params with the newParams and re-route to the new path.

// route def: /apps/:appId
// url: /apps/this-is-my-app?show=yes&color=red

FlowRouter.setParams({appId: "new-id"});
// Then the user will be redirected to the following path
//      /apps/new-id?show=yes&color=red

Just like FlowRouter.setParams, but for queryString params.

To remove a query param set it to null like below:

FlowRouter.setQueryParams({paramToRemove: null});

Get the current state of the router. This API is not reactive. You don't need to use this API most of the time. You can use reactive APIs like FlowRouter.getParam() and FlowRouter.getQueryParam() instead.

We have made this non reactive to reduce the unnecessary re-renders in your UI.

This gives an object like this:

// route def: /apps/:appId
// url: /apps/this-is-my-app?show=yes&color=red

var current = FlowRouter.current();
console.log(current);

// prints following object
// {
//     path: "/apps/this-is-my-app?show=yes&color=red",
//     params: {appId: "this-is-my-app"},
//     queryParams: {show: "yes", color: "red"}
// }

Sometimes we need to watch for the current route reactively. Avoid using this if possible.

Flow Router and Iron Router are two different routers. Iron Router tries to be a full featured solution. It tries to do everything including routing, subscriptions, rendering and layout management.

Flow Router is a minimalistic solution focused on routing with UI performance in mind. It exposes APIs for related functionality.

Let's learn more about the differences:

Flow Router doesn't handle rendering. By decoupling rendering from the router it's possible to use any rendering framework, such as Flow Layout to render with Blaze's Dynamic Templates, React, or Polymer. Rendering calls are made in the the route's action.

With Flow Router, you can register subscriptions, but there is no concept like Iron Router's waitOn. Instead Flow Router provides a reactive API to check the state of subscriptions. You can use that to achieve similar functionality in the template layer.

In Iron Router you can use reactive content inside the router, but any hook or method can re-run in unpredictable manner. Flow Router limits reactive data sources to a single run when it is first called.

We think, that's the way to go. Router is just a user action. We can work with reactive content in the rendering layer.

Router.current() is evil. Why? Let's look at following example. Imagine we've a route like this in our app:

/apps/:appId/:section

Now let's say, we need to get appId from the URL. Then we will do, something like this in Iron Router.

Templates['foo'].helpers({
    "someData": function() {
        var appId = Router.current().params.appId;
        return doSomething(appId);
    }
});

Okay. Let's say we changed :section in the route. Oh then above helper also gets rerun. Even if we add a query param to the URL, it gets rerun. That's because Router.current() looks for changes in the route(or URL). But in any of above cases, appId didn't get changed.

Because of this, a lot parts of our app gets re run and re-rendered. This creates unpredictable rendering behavior in our app.

Flow Router fixes this issue simply by providing the Router.getParam() API. See how to use it:

Templates['foo'].helpers({
    "someData": function() {
        var appId = FlowRouter.getParam('appId');
        return doSomething(appId);
    }
});

Flow Router has built in Fast Render support. Just add Fast Render to your app and it'll work. Nothing to change in the router.

For more information check docs.

Flow Router is a client side router and it does not support sever side routing at all. subscriptions are only run on the server to enabled Fast Render support.

Meteor is not a traditional framework where you can send HTML directly from the server. Meteor needs to send a special set of HTML to the client initially. So, you can't directly send something to the client your self.

Also, in the server we need look for different things compared with the client. For example:

• In server we've to deal with headers.
• In server we've methods like GET, POST, etc.
• In server we've Cookies

Although we may decide to enable server side rendering by running the actions and middlewares on the server, it's better to use a dedicated server-side router. meteorhacks:picker supports connect and express middlewares and has a very easy to use route syntax.