Design, develop and organize code

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§Why is pattern-matching so important?

Because it gives you a clean component model. This lets you build big things out of small things without ending up with spaghetti code.

The trick is to make composition easy. That way you can combine and extend microservices. Instead of modifying an existing microservice, simply add a new one with more functionality. This is a much more scalable way to handle changing requirements without building up technical debt.

There’s a great talk by Gerald Sussman (co-inventor of Scheme) on the basic principles of this idea. There’s also a maintainer blog post explaining this from a Seneca perspective.

A diamond is very pretty.
But it is hard to add to a diamond.
A ball of mud is not so pretty.
But you can always add more mud to a ball of mud.

Joel Moses / Paul Penfield

Some things that work well:

  • Separate the business logic from the execution. Put your business logic into separate plugins - either separate node modules, different repositories, or simply different files in the same repository.

  • Use execution scripts to compose your app. Don’t be afraid to use different scripts for different contexts. They should be pretty short any way. You want your scripts to look something like:

var SOME_CONFIG = process.env.SOME_CONFIG || 'some-default-value' 

require('seneca')({ some_options: 123 })

  // existing Seneca plugins
  .use('community-plugin-1', {some_config: SOME_CONFIG})

  // your own plugins with your own business logic

  .listen( ... )
  .client( ... )

  .ready( function() {
    // your own custom code - executed once Seneca is spun up

Things that don’t work well:

  • Mixing Seneca initialization with other framework initialization. Define your express or hapi app in one file, and Seneca in another. Keep it separate and simple.

  • Passing the Seneca instance around. Don’t create a Seneca instance and then pass it as a parameter to stuff you’ve required in, and only then start adding plugins and actions. Instead, use small execution scripts with clear and linear construction of your service from a list of plugins.

Looking for an example structure to copy? The nodezoo workshop is a good place to find one.

Issues? From spelling errors to broken tutorials and everything in between, report them here.