Native vs 3rd Party Promise Implementations

3 minute read

TIL that the promise implementation shipped with ES6 is not very performant, and that it is still preferable to use a 3rd party promise library for several reasons.

Note that this post will focus on the 3rd party promise library Bluebird

Why not Native?

I understood that pre-ES6 when there was no native promise implementation, 3rd party libraries were written to fill that gap. Now that native promises are available for use, why use a library to polyfill the behavior?

It appears that there are a few good reasons.

More Performant?

I stumbled across this StackExchange post which asks why native ES6 promises appear slower and less memory efficient than Bluebird promises. It points to a perf test that shows Bluebird promises are around 4x faster and use 4x less memory than native ES6 promises to resolve.

Farther down in that post the Bluebird author responds with some reasoning for the performance differences. The post was written in April of 2015, and after some additional searching I couldn’t tell if the performance data being referenced was still accurate. The performance test data referenced in the README of the bluebird repo was last updated in January of 2015.

I poked around a bit in the bluebird source and the author made it quite easy to re-run benchmarking. Check out the data below. I ran from the following branch which contains a fix for upgrading to the latest version of the “streamline” library (another 3rd party async javascript lib).

Dependency versions
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Benchmarking sequential (./bench doxbee)

results for 10000 parallel executions, 1 ms per I/O op

file                                       time(ms)  memory(MB)
callbacks-baseline.js                           118       30.55
callbacks-suguru03-neo-async-waterfall.js       174       43.49
promises-bluebird-generator.js                  213       38.16
promises-bluebird.js                            261       48.12
promises-cujojs-when.js                         357       61.63
promises-then-promise.js                        366       57.88
promises-lvivski-davy.js                        445       91.46
promises-tildeio-rsvp.js                        505       86.60
callbacks-caolan-async-waterfall.js             617       98.84
promises-dfilatov-vow.js                        671      147.82
promises-calvinmetcalf-lie.js                   828      138.86
promises-ecmascript6-native.js                 1123      183.64
generators-tj-co.js                            1170      137.32
promises-obvious-kew.js                        1215      214.58
promises-medikoo-deferred.js                   1841      164.09
observables-Reactive-Extensions-RxJS.js        2163      224.04
streamline-generators.js                       2262      180.45
streamline-callbacks.js                        3584      173.93
promises-kriskowal-q.js                       11226      835.02
observables-baconjs-bacon.js.js               34624      808.23
observables-pozadi-kefir.js                   56509      145.96
observables-caolan-highland.js               128962      457.45

Platform info:
Darwin 16.0.0 x64
Node.JS 6.7.0
Intel(R) Core(TM) i5-5257U CPU @ 2.70GHz × 4

Benchmarking parallel (./bench parallel) –p 25

results for 10000 parallel executions, 1 ms per I/O op

file                                      time(ms)  memory(MB)
callbacks-baseline.js                          268       64.71
promises-bluebird.js                           425       99.67
callbacks-suguru03-neo-async-parallel.js       431       82.30
promises-bluebird-generator.js                 494      103.07
promises-lvivski-davy.js                       740      157.46
promises-cujojs-when.js                        935      162.30
callbacks-caolan-async-parallel.js             943      147.88
promises-then-promise.js                      1408      312.29
promises-tildeio-rsvp.js                      1613      350.70
promises-calvinmetcalf-lie.js                 1745      369.84
promises-ecmascript6-native.js                2379      448.05
promises-dfilatov-vow.js                      2850      528.65
promises-medikoo-deferred.js                  4588      413.72
promises-obvious-kew.js                       5024      634.53
streamline-generators.js                     23243     1201.41
streamline-callbacks.js                      43371     1312.59

Platform info:
Darwin 16.0.0 x64
Node.JS 6.7.0
Intel(R) Core(TM) i5-5257U CPU @ 2.70GHz × 4

Looks like Bluebird still comes out on top for both speed and memory usage when compared to other promise implementations.

When compared to ES6, it is still 4.3x faster and 3.8x more memory efficient, at least under these test conditions.


Killer Feature: Promisify

Performance aside, Bluebird offers an awesome feature called promisification, which allows you to wrap another library and have it return promises instead! Examples from the docs:

var fs = require("fs");
// Now you can use fs as if it was designed to use bluebird promises from the beginning

fs.readFileAsync("file.js", "utf8").then(...)

You can do the same thing with database clients, or other async libraries that are not natively promise-based (and instead accept callbacks).

Also amazing!

Can I use?

According to can I use native promises are ready for use in most current version browsers today, but not all. If you’re looking to support legacy browsers (or IE), using a 3rd party promise library is a nice alternative to relying on an implementation in the browser.


It seems like of your 3rd party async-handling Javascript libraries, bluebird is still the best bet. It offers promisification and is more performant than native ES6 promises. I’ll be using it in my next project for sure.

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