Skip to content
/ promesse Public

A functional style Promises/A+ implementation that aims to be concise and clean.

Notifications You must be signed in to change notification settings


Folders and files

Last commit message
Last commit date

Latest commit



29 Commits

Repository files navigation


Build Status

Promises/A+ logo

Promesse is a Promises/A+ compliant Promise library. This implementation passes all the tests of the standard test suite.

Why oh Why?

I've written it because I love using promises in JS and I like to know how the tools I use work.

There are many implementations out there, I wanted mine to be very small and written as much as possible in functional programming style.

I'm rather happy about the result:

  • 98 lines of code (no comments, comments are for the weak), so probably one of the shortest implementations out there
  • looks a bit like Haskell :)

It's been a really enriching experience, now I know a lot more about the subtleties of promises than any documentation would tell.

Besides, working against an existing huge test suite is a cool programming exercise.

Obviously this is a toy project, but I'd be interested in having feedback on:

  • does the code make sense to you? or did I just write some "write-only" software?
  • can you see ways to make it smaller without making it too obscure / unreadable?
  • can you see other functional patterns that I could use to make the code more concise?


This is probably not very useful since promises are standard, but, if for some reason you need to:

npm i --save aplus-promesse


git clone
cd promesse
npm i
npm test

There are two test suites, the one from Promises/A+, and the one I wrote to help me when I did not understand the feedback from the official tests.

Making it Smaller

Now that the library is working and tested, I want to make it smaller in terms of number of lines of code.

The rules are:

  • lines must not exceed 80 columns
  • block declarations (by that I mean a declaration that takes more than one line or a succession of one line declarations) and top level declarations are followed with one blank line at least
  • more subjectively: the code needs to remain easy to read


A functional style Promises/A+ implementation that aims to be concise and clean.






No releases published


No packages published