thunkify-object

Build full object wrappers that convert regular node methods into methods that return a thunk, useful for generator-based flow control such as co.

Table of content

• Installation
• Examples
• Basic
• Pass Through
• Transformations
• Dealing with functions being both async and sync
• Events
• Running tests
• License

Installation

$ npm install thunkify-object --save

Examples

Basic

Let's say you have a constructor with async prototypes using callbacks.

function Dummy() {}

Dummy.prototype.hello = function(callback) {
  setImmediate(callback, null, 'Hello');
}

Dummy.prototype.helloYou = function(you, callback) {
  setImmediate(callback, null, 'Hello ' + you);
}

You first need to create the wrapper constructor once for all future instances.

var WrapperBuilder = require('thunkify-object').WrapperBuilder;

var DummyWrapper = new WrapperBuilder()
  .add(['hello', 'helloYou'])
  .getWrapper();

Let's use it with co.

var co = require('co');

co(function* () {
  // Instantiate your wrapper with an instance of the original
  var dummy = new DummyWrapper(new Dummy());

  var a = yield dummy.hello();
  console.log(a); // 'Hello'

  var b = yield dummy.helloYou('World');
  console.log(b); // 'Hello World'
});

Pass Through

If you want some functions not to change their behavior, you can use addPassThrough to simply inherit the function in your wrapper. This is usefull for synchronous functions that doesn't use callback.

var WrapperBuilder = require('thunkify-object').WrapperBuilder;

var DummyWrapper = new WrapperBuilder()
 .add(['hello', 'helloYou'])
 .addPassThrough('helloSync')
 .getWrapper();

Transformations

For complex objects, the WrapperBuilder can apply transformations to callback parameters.

Let's wrap the MongoDB native driver as an example.

var WrapperBuilder = require('thunkify-object').WrapperBuilder;

var Collection = new WrapperBuilder()
 .add(['add', 'count', 'findOne'])
 .getWrapper();

var Db = new WrapperBuilder()
  .add('collection', {
    transformations: {
      1: function(col) { return new Collection(col); }
    }
  })
  .getWrapper();

var MongoClient = new WrapperBuilder()
  .add('connect', {
    transformations: {
      1: function(db) { return new Db(db); }
    }
  })
  .getWrapper();

Now that you have your wrappers, you can use them like that.

var mongodb = require('mongodb');

function* foo(url) {
  var mongoClient = new MongoClient(mongodb.MongoClient);

  // returned db is a wrapper
  var db = yield mongoClient.connect(url);

  // returned collection is a wrapper
  var collection = yield db.collection('documents');

  yield collection.add({ _id: 1, name: 'Paul Valery' });
  return yield collection.findOne({ _id: 1 });
}

Let's use it with co.

var co = require('co');

co(function* () {
  var doc = yield foo('mongodb://localhost:27017/myproject');
  console.log(doc);
});

Dealing with functions being both async and sync

Sometimes functions have an optional callback parameter (like this MongoDB driver method). That means when you call it with a callback it's async, but when you call it without a callback it's sync (potentially returning a value).

Here is how to wrap those functions.

var WrapperBuilder = require('thunkify-object').WrapperBuilder;

var Wrapper = new WrapperBuilder()
 .add('helloWithOptionalCallback', {
   sync: true
 })
 .getWrapper();

Any wrapper instance will have 2 explicit methods:

• helloWithOptionalCallback which is async, returning a thunk
• helloWithOptionalCallbackSync which is sync (note the Sync suffix)

The synchronous prototype can be customized with a specific name format and a transformation.

var WrapperBuilder = require('thunkify-object').WrapperBuilder;

var Wrapper = new WrapperBuilder()
 .add('helloWithOptionalCallback', {
   sync: {
     prototypeNameFormat: '%sCustomSuffix',
     transformation: function(res) {
       return res;
     }
   }
 })
 .getWrapper();

Events

var WrapperBuilder = require('thunkify-object').WrapperBuilder;

var Wrapper = new WrapperBuilder()
 .addEvent(['on', 'once'])
 .addPassThrough('emit')
 .getWrapper();

var EventEmitter = require('events').EventEmitter;
var co = require('co');

co(function* () {

  var e = new Wrapper(new EventEmitter());

  setTimeout(function() {
    e.emit('finish', 'Finish data');
  }, 200);


  var res = yield e.on('finish');
  console.log(res); // 'Finish data'
});

Note that you can still pass a listener as a callback:

var EventEmitter = require('events').EventEmitter;
var co = require('co');

co(function* () {

  var e = new Wrapper(new EventEmitter());

  setTimeout(function() {
    e.emit('finish', 'Finish data');
  }, 200);


  e.on('finish', function(res) {
    console.log(res); // 'Finish data'
  });
});

If you need transformations, you can define them for each event:

var WrapperBuilder = require('thunkify-object').WrapperBuilder;

var Wrapper = new WrapperBuilder()
 .addEvent(['on', 'once'], {
   events: {
     'finish': transformations: {
       0: function(arg) { return ... },
       1: function(arg) { return ... }
     }
   }
 })
 .addPassThrough('emit')
 .getWrapper();

Running tests

$ make test

With code coverage.

$ make test-cov

License

Thunkify-object is freely distributable under the terms of the MIT license.