async-done

Allows libraries to handle various caller provided asynchronous functions uniformly. Maps promises, observables, child processes and streams, and callbacks to callback style.

As async conventions evolve, it is useful to be able to deal with several different styles of async completion uniformly. With this module you can handle completion using a node-style callback, regardless of a return value that's a promise, observable, child process or stream.

Usage

Successful completion

var asyncDone = require('async-done');

asyncDone(
  function (done) {
    // do async things
    done(null, 2);
  },
  function (error, result) {
    // `error` will be null on successful execution of the first function.
    // `result` will be the result from the first function.
  }
);

Failed completion

var asyncDone = require('async-done');

asyncDone(
  function (done) {
    // do async things
    done(new Error('Some Error Occurred'));
  },
  function (error, result) {
    // `error` will be an error from the first function.
    // `result` will be undefined on failed execution of the first function.
  }
);

API

`asyncDone(fn, callback)`

Takes a function to execute (fn) and a function to call on completion (callback).

`fn([done])`

Optionally takes a callback to call when async tasks are complete.

Completion and Error Resolution

Callback (done) called
- Completion: called with null error
- Error: called with non-null error
Stream or EventEmitter returned
- Completion: end-of-stream module
- Error: domains
- Note: Only actual streams are supported, not faux-streams; Therefore, modules like event-stream are not supported.
Child Process returned
- Completion end-of-stream module
- Error: domains
Promise returned
- Completion: onFulfilled method called
- Error: onRejected method called
Observable (e.g. from RxJS v5 or RxJS v4) returned
- Completion: complete method called
- Error: error method called

Warning: Sync tasks are not supported and your function will never complete if the one of the above strategies is not used to signal completion. However, thrown errors will be caught by the domain.

`callback(error, result)`

If an error doesn't occur in the execution of the fn function, the callback method will receive the results as its second argument. Note: Some streams don't received any results.

If an error occurred in the execution of the fn function, The callback method will receive an error as its first argument.

Errors can be caused by:

A thrown error
An error passed to a done callback
An error event emitted on a returned Stream, EventEmitter or Child Process
A rejection of a returned Promise - If the Promise is not rejected with a value, we generate a new Error
The onError handler being called on an Observable