Dependency injection

We have built our own super simple DI.

Install

npm install @mindhive/di

Motivations and benefits

• Prefer pure functions
• Avoid ES6 imports as they are difficult to test
• Especially avoid Meteor package imports as most test runners don't understand Meteor's packaging (they can be accessed through Meteor globals but that's not a great idea either)

Lifecycle

1. Main file for the app should import all of it's modules using initModules()

2. Modules should export a default function

   • For example: export default () => { ...; return { serviceName: new Service(), ... } }
   • Return an object where the keys map service names to the service objects/functions to be put into the app context
   • Modules further down thru the array passed to initModules() can use services added to the appContext by earlier modules. The module function is passed the current appContext (destructing works a treat), for example: export default ({ Meteor, Mongo }) => { ... }
   • Modules don't have to return anything, you can use them to perform other initialization
   • Modules are called inside Meteor.startup so there is no need to manage that yourself

3. To access services in the appContext call app() to get the appContext

Testing

In the example below service will be the only object in the appContext and available to any code that calls app().

import { mockAppContext } from '@mindhive/di'
const modules = () => ({ 
  service: { foo: sinon.spy() }  
}) 
it('should call service.foo()', 
  mockAppContext(modules, () => { 
    funcUnderTest()
    service.foo.should.have.been.calledOnce      	
  })
)

modules is a function so that the spys and dummy values used in it are recreated every test, avoiding any contamination to the next test.

However, if your test runner doesn't teardown the tests properly it may be necessary to use resetAppContext.

You can also use initModules within the 'modules' function, it operates exactly as it would in production code.