Synchronisify

Turns asynchronous constructor into synchronous one.

npm install synchronisify

Why?

Often we want to do asynchronous action directly in constructor of a object:

class DatabaseClient {
    constructor(connectionString) {
        // connect to database
        // what should we return here?
    }
}

the problem is that if we return here a promise usage of our object will be... weird:

new DatabaseClient('me@localhost/myDatabase').then((db) => {/* do something */})

What we can do is to make async action 'in background' and make sure in each method of a class waits for initialization to finish. This is exactly was synchronisify makes easier.

There are also different options like static method, read this StackOverflow thread for more.

Example

synchronisify helps programmers to build clean public interface.

const synchronisify = require('../lib/lib')

const delay = (t = 1000) => new Promise(resolve => setTimeout(resolve, t))

@synchronisify //yay, it support es7 decorators. If you don't use es7 just wrap your class like this: synchronisify(ApiClient)
class ApiClient {
  constructor (login, pass) {
    this.login = login
    this.pass = pass
    // simulate api call for auth key
    this._init = delay().then(() => { this.apiKey = 'SECRET_API_KEY' })
  }

  action () {
    if (!this.apiKey) {
      throw new Error()
    }

    // do something
  }
}

const client = new ApiClient('login', 'pass') // constructor itself is synchroneus
client.action() // action method code will run after init is done

How?

Each method in prototype is wrapped in initPromise.then(method). Drawback is that each method becames async i.e. it returns promise.

Docs

function synchronisify (asyncClass, initPromiseName = '_init')