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In this part of the Meiosis tutorial, we will look at routing. We'll use the simple page navigation example shown below.


Start Without Routing

Routing does not have to be so notoriously difficult and complicated. We'll start implementing the application without routing, using the model as our single source of truth (as always) and actions to navigate to different pages. Then, we can add routes as simple mappings to actions.

Defining Navigation

To identify the different pages of the application, we'll use simple constants:

export const pages = {
  home: { id: "Home", tab: "Home" },
  coffee: { id: "Coffee", tab: "Coffee" },
  beer: { id: "Beer", tab: "Beer" },
  beerDetails: { id: "BeerDetails", tab: "Beer" }

Then, to navigate, we can create a navigation object with convenient functions to navigate to different pages. We'll assign the current page and parameters to the model. Thus the model identifies the current location.

export const createNavigation = update => {
  const navigate = (page, params = {}) =>
    update(model => Object.assign(model, ({ page, params })));

  const navigateToBeer = () => {
    services.loadBeer().then(beerList => {
      update(model => Object.assign(model, { beerList }));
  return { navigateToHome, navigateToBeer, ... };

Notice that we can also define what needs to happen when navigating to a page, such as loading data from the server. Callers of these functions don't need to know what must happen when navigating to a page.

Creating the App

When creating the app, we'll pass the navigation object over so that we can call its functions and navigate. Since the model identifies the current page, we'll create a lookup map to conveniently find the corresponding component. Then we can just call its view function to render the current page.

export const createApp = (update, navigation) => {
  const homeComponent = createHome(update); //more...
  const pageMap = {
    []: homeComponent, //more...
  return {
    view: model => {
      const component = pageMap[];
      return (
        // render tabs, determines active tab

Adding Routes

Adding routes is a simple mapping between route and a plain object with the page id and the navigation action:

export const createRouter = navigation => {
  const routes = {
    "/": { id:,
      action: navigation.navigateToHome },
    "/coffee/:id?": { id:,
      action: navigation.navigateToCoffee },
    "/beer": { id:,
      action: navigation.navigateToBeer },
    "/beer/:id": { id:,
      action: navigation.navigateToBeerDetails }

We can use a simple routing library such as url-mapper to resolve routes:

import Mapper from "url-mapper";

const resolveRoute = () => {
  const route = document.location.hash.substring(1);
  const resolved =, routes);
  if (resolved) {

window.onpopstate = resolveRoute;

Once a route is resolved, we can call its action function to navigate to the page.

Route Sync

Everything works now, except for one detail: although navigating with actions or routes works the same way, navigating with an action does not reflect the corresponding route in the browser's location bar.

We can fix this with a simple route sync function:

const routeMap = Object.keys(routes).reduce((result, route) => {
  result[routes[route].id] = route;
  return result;
}, {});

const routeSync = model => {
  const segment = routeMap[] || "/";
  const route = urlMapper.stringify(segment, model.params||{});
  if (document.location.hash.substring(1) !== route) {
    window.history.pushState({}, "", "#" + route);

After building a page id to route lookup map, we can use it along with url-mapper's stringify function to generate the route from the model's current page id. Then, if the browser's location bar does not match the route, we can set it with window.history.pushState.

Now, we can use actions and routes to navigate, and the browser's location bar reflects the correct route. The model is our source of truth: in fact, we can even change the model by typing in the textarea of the Meiosis Tracer, and see the correct route in the browser's location bar along with the correct page in the view.

Up Next

In the next section, we'll try a different routing library, Universal Router.

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Meiosis is developed by @foxdonut00 / foxdonut and is released under the MIT license.