24 September 2016

Connecting to Elixir web channels from the Angular 2 quickstart application

I am busy learning Elixir, a language that adds syntactic sugar to the awesomely scalable and concurrent Erlang language.  The "go to" framework in Elixir is Phoenix and I'm busy writing my "hello world" application which will serve up data across a web channel.

I followed the Typescript version of the Quickstart guide for Angular 2 (here).  I really like what I've seen of Typescript so far.  Dependencies are easy to manage and the ability to define interfaces is a good sign of how well structured the language is.  I think Satya Nadella should be made an open source hero, if such an award exists.

Anyway, what I wanted to do was get my Angular 2 application to be able to connect to the Elixir server channel and send a request to listen to a particular stream.  The idea is to use the Actor concurrency model (explained brilliantly in "The Little Elixir & OTP Book") to start up a new process whenever a request for a stream arrives.  This article focuses on setting up the Angular 2 connection.

The official Phoenix javascript client is packaged up and can be installed with "npm install --save phoenix".  Once it's installed we need to tell SystemJS where to find it so we amend systemjs.config.js and include it in our map array.

Now we'll be able to import the Phoenix class from it wherever we need to. We'll need it in the service that we're going to use to wrap the Phoenix channel support. Lets take a look…

We import the library using the map name that we set up in our systemjs config to make it available to our class.  We then copy the code that Phoenix shows on the channels manual page to actually handle the connection.

This gives us a channel service that we'll be able to inject into components.

Angular 2 uses constructor injection so we'll be passing a channel service into the constructor function. Before we do that though we need to let the component know that our channel service is a provider so that we can properly typecast the injected variable. Once all this is saved run your app with 'npm start' and if you pop over to your browser window you should see error messages in your console log saying that the channel connection was refused, unless of course you're already running your Phoenix server.
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