zerostep

ZeroStep is a small library to organize, wire and manage the lifecycle of modules.

Features

• Initialize and destroy modules
• Import and export services from modules
• Check imports/exports at registration time
• Take care of process signals for SIGTERM, SIGINT and SIGUSR2 if wished
• Plays nice with nodemon
• Zero dependencies
• Promise based
• Gracefully handle error conditions in module initialization/destruction

Examples

Shortcuts

'use strict'

const ZeroStep = require('../index')

const zs = new ZeroStep()

zs
  .register((() => {
    let secret = 'S3C43T'
    let obj = {
      destroy: () => console.log(`Destroying obj with secret:= ${secret}`),
    }

    return {
      name: 'Secret and initValue usage in destroy',
      init: () => obj,
      destroy: (ctx, obj) => obj.destroy(),
    }
  })())
  .register({
    name: 'Module which was added by chaining register calls!',
    init: () => console.log('Hello from chained module!'),
  })


zs.init().then(() => zs.destroy())

Will print:

ZeroStep:- Initializing module Secret and initValue usage in destroy() -> []
ZeroStep:- Initializing module Module which was added by chaining register calls!() -> []
Hello from chained module!
ZeroStep:- Destroying module Module which was added by chaining register calls!
ZeroStep:- Destroying module Secret and initValue usage in destroy
Destroying obj with secret:= S3C43T
ZeroStep:- Destroyed all modules

Hello, world

const ZeroStep = require('zerostep')

const zs = new ZeroStep()

zs.register({
  name: 'hello-world',
  init: () => console.log('hello, world'),
  destroy: () => console.log('goodbye, world')
})

zs.init().then(() => zs.destroy())

Will print:

ZeroStep:- Initializing module hello-world() -> []
hello, world
ZeroStep:- Destroying module hello-world
goodbye, world

Usage of declarative env attribute

const ZeroStep = require('../index.js')

const zs = new ZeroStep()

zs.register({
  name: 'hello-world',
  env: [
    {
      name: 'message',
      // optional attributes
      default: 'Hello, world!',
      valid: (value) => value === 'Hello, world!',
      showValue: true,
      hint: 'Please provide a message to display to the user'
    }
  ],
  init: (ctx) => console.log(ctx.env.message),
})

zs.init().then(() => zs.destroy())

Will print:

ZeroStep:- Module hello-world env[message] := <Hello, world!>
ZeroStep:- Initializing module <hello-world>() -> []
Hello, world!
ZeroStep:- Initialization of all registered modules completed successfully for <ZeroStep>
ZeroStep:- Destroying module hello-world
ZeroStep:- Destroyed all modules for <ZeroStep>

Two modules

const ZeroStep = require('zerostep')

const zs = new ZeroStep()

zs.register({
  name: 'one',
  export: 'symbolFromOne',
  init: () => {
    console.log('hello from 1')
    return 'Message from one'
  },
  destroy: () => console.log('goodbye from 1')
})

zs.register({
  name: 'two',
  imports: ['symbolFromOne'],
  init: (ctx) => {
    console.log('hello from 2')
    console.log(`got ${ctx.symbolFromOne}`)
  },
  destroy: () => console.log('goodbye from 2')
})

zs.init().then(() => zs.destroy())

Will print:

ZeroStep:- Initializing module one() -> [symbolFromOne]
hello from 1
ZeroStep:- Initializing module two(symbolFromOne) -> []
hello from 2
got Message from one
ZeroStep:- Destroying module two
goodbye from 2
ZeroStep:- Destroying module one
goodbye from 1

Note Module two gets initialized after module one but destroyed before module one. This is almost always what you want!

Documentation

ZeroStep.constructor(options)

• You can provide the following options
  • name -> Defaults to ZeroStep
  • loggerCb -> (name) -> {info: (msg) -> void, error: (msg) -> void}
  • env -> Object. Defaults to process.env.

Create a new instance.

ZeroStep.prototype.register(module) -> ZeroStep(this)

• module must have a name attribute and the method attribute init
  • name (string): name of the module
  • init ((ctx) => {}) : is called to initialize the module with its context object and must return a non null/undefined value if optional export attribute is set
• module has optional attributes
  • env ([envDeclarations*]): a list which declares what environment variables this module needs
    • must have attributes
      • name (string): name of the environment variable
    • optional attributes
      • hint (string): helpful hint to be displayed when the environment variable is not set
      • valid ((value) => boolean): valid is called with the actual value of the environment variable and must return true if the value is valid
      • default (string|number): default value to be used if the environment variable is not provided
      • showValue (boolean): show the actual value of the environment variable which will be provided to the module (defaults to true)
  • export: string which names the value returned by init
  • imports: an array of string names which named exports of other modules should be importet. IMPORTANT: every name must have been registered in an export attribute before
  • destroy: is called to destroy the module with its context object as first and the return value of its init method as second argument

Note The context object for init/destroy is created once for the init method and provided to the destroy method Note You can get a handle to destroy an object by just returning it from init - it will be provided to destroy w/o a need to export it

ZeroStep.prototype.init() -> Promise

Initialize all registered modules in the order of their registration.

See ZeroStep.prototype.initAsApplicationCore() if you want ZeroStep to take care of SIGINT, SIGTERM and SIGUSR2.

ZeroStep.protoype.destroy() -> Promise

Destroy all registered modules in the opposite order in which they where registered.

ZeroStep.protoype.initAsApplicationCore() -> Promise

Registers a handler for disconnect, uncaughtException, unhandledRejection, error, SIGINT, SIGTERM and SIGUSR2 which will call ZeroStep.prototype.destroy() and calls ZeroStep.prototype.init().

Contributing

Pull requests are welcome. Please write tests for your changes & run npm test before making a pull request.

Contributors & Thanks

• Bernard Pletikosa - feedback on design and supporting ZeroStep from the start
• Jeff Hiltz - support and initiative to make ZeroStep open source
• relayr - allowing to open source ZeroStep