The-holder NPM

The Holder

General app loader or item holder.

Introduction

Generally speaking, the backbone of an app takes the following responsibilities:

correctly load aspects (items) the app cares about
- config, context, components ...
- items usually have dependencies from here to there, thus the dependencies of an item must be loaded before it
- any item should have access to its dependencies
correctly close the app
- the ability to stop receiving any request from outside world while keep handling already received requests until they finished to support graceful shutdown
- the ability to destroy items and release all resources

The Holder takes and only takes tasks listed above. The detailed logic, such as what items should be load, what're their dependencies, how should they be stopped and destroyed, is left blank to the user.

Installation

npm install the-holder

Usage

// define your app
const definitions = [
  {name: 'config', build: () => {...load config... return {item: config}}},
  {
    name: 'db', 
    need: 'config', 
    build: async ({config}) => {
      ...connect to db... 
      return {
        item: connection,
        destroy: async () => {...disconnect...}
      }
    }
  },
  {
    name: 'server',
    need: 'config',
    build: async ({config}) => {
      ...start (such as http) server... 
      return {
        item: server,
        stop: async () => {...stop receiving requests...}
      }
    }
  },
  {
    name: 'handlers',
    need: ['config', 'db', 'server'],
    build: ({config, db, server}) => {
      ...register handlers to the server...
      ...no need to return anything...
    }
  }
]

// start app (holder)
const Holder = require('the-holder')
const holder = new Holder()
await holder.load(definitions)

// setup graceful shutdown
const gracedown = require('grace-down')
gracedown(async () => {
  await holder.close()
  process.exit(0)
})