A set of high performance yield handlers for Bluebird coroutines
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README.md

bluebird-co

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A set of high performance yield handlers for Bluebird coroutines.

Description

bluebird-co is a reimplementation of tj/co generator coroutines using bluebird, Bluebird.coroutine and Bluebird.coroutine.addYieldHandler to insert a yield handler that can transform all the same yieldable value types as tj/co and more.

Yieldable Types include arrays of promises, objects with promises as properties, thunks, other generators, and even ES6 iterables. Plus bluebird-co allows for additional yield handlers to be added that work together in combination with all the existing yield handlers.

Combined with Babel's async-to-module-method (or bluebirdCoroutines in Babel 5) transformer, you can write easy and comprehensive async/await functions.

Quickstart

To install: npm install bluebird-co

Ensure Bluebird is installed: npm install bluebird@3

Performance

Squeezing the most performance out of every asynchronous operation was a high priority for bluebird-co, and as a result it is much faster than tj/co in essentially every scenario.

See here for detailed benchmarks

Usage

bluebird-co includes Bluebird as a peer dependency so that it will use any already installed instance of Bluebird, making it easier to bootstrap and integrate.

Using automatic bootstrapping:

require('bluebird-co');

and done.

Alternatively, manually adding the yield handler to Bluebird:

var Promise     = require('bluebird'),
    bluebird_co = require('bluebird-co/manual');

Promise.coroutine.addYieldHandler(bluebird_co.toPromise);

var fn = Promise.coroutine(function*(){
    //do stuff
});

fn().then(...);

In the automatic bootstrapping version, it actually executes the same first four lines of code as above to add the yield handler. Bluebird-co provides manual bootstrapping for control over the process if desired.

Usage with Babel 6:

Babel 6 provides the transform-async-to-module-method plugin which can pass a generator to a function to convert it to an asynchronous coroutine. Using bluebird-co instead of the default Bluebird install will automatically bootstrap the yield handler while remaining completely transparent.

.babelrc file

{
    "plugins": [
        ["transform-async-to-module-method", {
            "module": "bluebird-co",
            "method": "coroutine"
        }]
    ]
}

ES7 file to be transformed

async function fn() {
    //do stuff
}

fn().then(...);

Example coroutines

Note: bluebird-co has to be added to Bluebird via automatic bootstrapping or manual addition before these snippets can work.

var Promise = require('bluebird');
var fs = Promise.promisifyAll(require('fs'));

var myAsyncFunction = Promise.coroutine(function*() {
    var results = yield [Promise.delay( 10 ).return( 42 ),
                         readFileAsync( 'index.js', 'utf-8' ),
                         [1, Promise.resolve( 12 )]];

    console.log(results); //[42, "somefile contents", [1, 12]]
});

myAsyncFunction().then(...);

ES7 version

import Promise from 'bluebird';
import {readFile} from 'fs';

let readFileAsync = Promise.promisify(readFile);

async function myAsyncFunction() {
    let results = await [Promise.delay( 10 ).return( 42 ),
                         readFileAsync( 'index.js', 'utf-8' ),
                         [1, Promise.resolve( 12 )]];

    console.log(results); //[42, "somefile contents", [1, 12]]
}

myAsyncFunction().then(...);

tj/co drop-in replacement

import {co} from 'bluebird-co';

co(...);
co.wrap(...);
For more examples, see the tj/co README and the Bluebird Coroutines API.

Yieldable Types

  • Promises
  • Arrays
  • Objects
  • Generators and GeneratorFunctions
  • Iterables (like new Set([1, 2, 3]).values())
  • Functions (as Thunks)
  • Custom data types via [.addYieldHandler(fn)#addyieldhandlerfn--function
  • Any combination or nesting of the above.

Custom yieldable types

It may become desirable to add custom yield handling for types not listed above based on the needs of a certain application. To make this easy, bluebird-co provides an analogue to Bluebird's Bluebird.coroutine.addYieldHandler that works together in combination with the above yield handlers.

To do this, bluebird-co provides the .coroutine.addYieldHandler(fn) function, or just .addYieldHandler(fn) for short. The first is for strict compatibility with Bluebird.

Example of automatically fetching model data by yielding the model instance:

import {coroutine} from 'bluebird-co';

class MyModel {
    async fetch() {
        //do stuff
        return data;
    }
}

coroutine.addYieldHandler(function(value) {
    if(value instanceof MyModel) {
        return value.fetch();
    }
});

async function test() {
    let model = new MyModel();

    let data = await model; //calls model.fetch() and waits on it.
}

Additionally, you can even access the array of yield handlers manually if you ever need to remove one, like so:

console.log(coroutine.yieldHandlers); //array of functions

Caveats:

Although this works for most classes and even null, it will NOT work if the class inherits from Object or if Object is in the prototype chain for the value's constructor. If it inherits from Object, it will be considered an Object instance and processed like any other object. Values without any constructor property will be considered an Object, as well.

API

All functions and properties listed below are exported by the bluebird-co module.


.toPromise(value : any) -> Promise<any> | any

toPromise is the central function of bluebird-co. It takes any of the supported yieldable types (and those added via .addYieldHandler), and attempts to convert it to a Promise. Any Promises within the value are resolved before the returned Promise resolves.

In the event that the given value cannot be transformed into a Promise, like when it is not in the possible yieldable types, the original value is returned. When used in conjunction with Bluebird coroutines, Bluebird will throw an error because the value is not a Promise instance.


.addYieldHandler(fn : Function)

alias: .coroutine.addYieldHandler(fn : Function)

Very similar to Bluebird.coroutine.addYieldHandler, .addYieldHandler allows custom types to be processed by bluebird-co in conjunction with any other yieldable types, even other custom yield handlers. This includes nested yieldable types.

Aside from the caveats of Object types when using custom yield handlers, any other type or value can be handled, even null, undefined, Symbols, anything. However, built-in yield handlers cannot be overridden.

See the above section on Custom yieldable types for an example.


.coroutine(gfn :GeneratorFunction) -> Function

alias: .wrap(gfn :GeneratorFunction) -> Function

alias: .co.wrap(gfn :GeneratorFunction) -> Function

This calls Bluebird.coroutine and returns the resulting function. When called, the returned function will return a Promise.

The .wrap alias is provided to be a drop-in replacement for co.wrap.


.execute(gfn :GeneratorFunction|Generator, ...args : any[]) -> Promise<any>

alias: .co(gfn :GeneratorFunction|Generator, ...args : any[]) -> Promise<any>

This calls .coroutine, then invokes the resulting function with the arguments provided, or just runs the generator object directly.

It is meant as a drop in replacement for tj/co co, like so:

//import {co} from 'bluebird-co';
var co = require('bluebird-co').co;

function* do_stuff(num) {
    return num;
}

co(do_stuff, 10).then(function(result){
    console.log(result); //10
});

.coroutine.yieldHanlders -> Array<Function>

Exposes all custom yield handlers that have been added.

bluebird-co expects this to be an array, so don't overwrite it with something silly.


.isThenable(value : any) -> boolean

alias: .isPromise(value : any) -> boolean

function isThenable(value) {
    return value && typeof value.then === 'function';
}

.isGenerator(value : any) -> boolean

Checks if the value is a generator instance with .next and .throw.


.isGeneratorFunction(value : any) -> boolean

Checks if the value is a GeneratorFunction.


Changelog

2.2.0
  • Allow .co to accept generators and generator functions like tj/co does. (thanks pkaminski)
2.1.2
  • Add .co.wrap alias for .wrap
2.1.1
  • Add simple quickstart section to README
  • Add usage docs with Babel 6
2.1.0
  • Added .execute/.co functions.
  • (BUILD)(FIXED) As of this release, the build is failing only because Babel runtime is screwed up.
2.0.0
  • Improve docs
  • Upgrade to Bluebird 3.0
  • Upgrade to Babel 6 for build system
  • (MAJOR) Change behavior of classes that inherit from Object
  • Small internal improvements
1.3.1 - 1.3.2
  • Significantly improve performance of iterables.
1.3.0
  • Basic support for Iterables
1.2.0
  • Allow manual addition of the yield handler via requiring bluebird-co/manual
  • Exposed toPromise function in extra API
1.1.2 - 1.1.12
  • Optimizations and bugfixes
1.1.1
  • Don't export isNativeObject, because it isn't generic enough to use in most places, only internally under the right circumstances.
1.1.0
  • Differentiate between native objects and class instances. Fixes addYieldHandler functionality when used with class instances, but does not accept class instances as objects when there is not a handler for them.
1.0.0 - 1.0.5
  • Initial releases, documentation and bugfixes.

License

The MIT License (MIT)

Copyright (c) 2015 Aaron Trent

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.