This page covers Elm 0.18

Routing introduction

Let's add a routing to our application. We will be using the Elm Navigation package and UrlParser.

• Navigation provides the means to change the browser location and respond to changes
• UrlParser provides route matchers

First install the packages:

elm package install elm-lang/navigation
elm package install evancz/url-parser

Navigation is a library that wraps Html.program. It has all the functionality of Html.program plus some extra things:

• Listens for location changes on the browser
• Triggers a message when the location changes
• Provides ways of changing the browser location

Flow

Here are a couple of diagrams to understand how routing will work.

Initial render

• (1) When the page first loads the Navigation module will fetch the current Location and send it to the application init function.
• (2) In init we parse this location and get a matching Route.
• (3, 4) We then store this matched Route in our initial model and return this model to Navigation.
• (5, 6) Navigation then renders the view by sending this initial model.

When the location changes

• (1) When the browser location changes the Navigation library receives an event
• (2) A OnLocationChange message is sent to our update function. This message will contain the new Location.
• (3, 4) In update we parse the Location and return the matching Route.
• (5) From update we return the updated model which contains the update Route.
• (6, 7) Navigation then renders the application as normal