bluebird-co

A set of yield handlers for Bluebird coroutines.

Description

This is a port of tj/co generator coroutines to bluebird using Bluebird.addYieldHandler to add in a yield handler that can transform all the types of yieldable values tj/co can into normal promises to resolve.

Combined with Babel's bluebirdCoroutines transformer, you can write easy and comprehensive async/await functions.

Performance

Given Bluebird's fame for high performance promises, it should come as no surprise that bluebird-co can achieve up to a couple orders of magnitude better performance on some particular tasks than tj/co, with most coroutines being about two to eight times faster with bluebird-co.

See here detailed benchmarks

Usage

require('bluebird-co') and done.

Usage in detail (to ensure everything works)

bluebird-co works by requiring bluebird and calling Bluebird.coroutine.addYieldHandler to add the appropriate functionality.

However, to ensure everything works you will need to install bluebird before any other module, so it exists in your node_modules folder. Then when you install any other module, including bluebird-co, they will require the already installed copy of bluebird instead of installing another, independent copy in their own node_modules folder.

Likewise, if you intend to override co.wrap, you will have to install co before any module that relies on co, that way koa and the like will use it instead of installing their own copy.

Your package.json should look something like this:

{
    "...": "...",
    "dependencies": {
        "bluebird":     "^2.9.33",
        "co":           "^4.5.4",
        "bluebird-co":  "^1.0.2"
    },
    "...": "..."
}

before installing any other module that relies on those.

#####NOTE: Before you delete your package.json out of frustration You can achieve the desired state of your node_modules by simply installing bluebird, co optionally, then bluebird-co, saving them to your package.json, then deleting your node_modules folder. Then run npm install, and it'll install your dependencies without duplicates.

Example coroutine

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(...);

For more examples, see the tj/co README and the Bluebird Coroutines API.

Overriding co.wrap

In my own experience, mixing bluebird coroutines and co/co.wrap can result in less than savory stack traces and other things. Here is a simple way to override almost all common usages of the co library.

var Promise = require('bluebird');
var co = require('co');

co.wrap = function(fn) {
    return Promise.coroutine(fn);
}

I've been using this method with Koa and a few other libraries for a while now and it seems to work. However, if a library invokes co directly, it will fail to replace that.

Extra API

#####BluebirdCo.addYieldHandler(handler : Function) Although this library comes with enough handlers for most occasions, you might need more specific handling of some types that the library cannot handle by default. BluebirdCo.addYieldHandler works basically the same as the normal Bluebird.addYieldHandler function but interoperates fully with the rest of BluebirdCo's handlers.

Example:

import Promise from 'bluebird';
import BluebirdCo from 'bluebird-co'; //Automatically adds most yield handlers

class MyModel {
    async function fetch() {
        //some async work...
    }
}

BluebirdCo.addYieldHandler(value => {
    if(value instanceof MyModel) {
        return value.fetch();
    }
});

async function getData() {
    let data = await {
        model1: new MyModel('something'),
        model2: [new MyModel(1), new MyModel(2)]
    };
    
    console.log(data); //{model1: 'something result', model2: ['result 1', 'result 2']}
}

getData().then(...);

you get the idea.

The normal behavior when yielding unknown values is either to throw an error if it's on the top level (the object in the above example), or to silently ignore it and return it unchanged if it was within an array or object, etc.

Adding a custom yield handler would allow you to define new behavior for handling unknown types, like automatically fetching data from models in the above example.

#####BluebirdCo.isThenable(value : any) -> boolean Alias: isPromise

Return true if the value has a .then function or is an instance of Promise

#####BluebirdCo.isGenerator(value : any) -> boolean

Returns true if the value is an instance of a generator.

#####BluebirdCo.isGeneratorFunction(value : any) -> boolean

Returns true if the value is a generator function that when called will create a new generator instance.

Changelog

#####1.1.2 - 1.1.11

• 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.