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1.0.9 • Public • Published


A library for Communicating Sequential Processes in Node.js, built on top of async/await.

npm version


This library requires async/await support in your Node.js runtime, so ideally node>=7.4.

$ npm install --save @paybase/csp


$ yarn add @paybase/csp

Example Usage

Below is a trivial example of usage, that plays on the standard ping-pong example.

const { channel, put, take } = require('@paybase/csp');
const timeout = ms => new Promise(resolve => setTimeout(resolve, ms));
const wiff = channel();
const waff = channel();
const createBall = () => ({ hits: 0, status: '' });
const createBat = async (inbound, outbound) => {
  while (true) {
    const ball = await take(inbound); // wait for an incoming ball
    ball.status = ball.status === 'wiff!' ? 'waff!' : 'wiff!';
    console.log(`🎾  Ball hit ${ball.hits} time(s), ${ball.status}`);
    await timeout(500); // assume it's going to take a bit to hit the ball
    await put(outbound, ball); // smash the ball back
createBat(waff, wiff); // create a bat that will wiff waffs
createBat(wiff, waff); // create a bat that will waff wiffs
put(waff, createBall());

ping pong


This library exposes 5 functions and one factory.


This factory method constructs a new channel and returns it. A channel contains no publicly accessible properties, but contains information about interactions with the channel.

const chan = channel();

put(channel, message) -> Promise

The put function requires the channel on which to put the supplied message. The put method returns a Promise which can be optionally awaited and will resolve when something is ready to take the message from the channel.

const chan = channel();
put(chan, 42);
// ...or...
await put(chan, 42);

take(channel) -> Promise

The take function requires the channel to take from. The take method returns a Promise which should always be awaited and will resolve with a message, when a message is available.

const chan = channel();
put(chan, 42);
const msg = await take(chan); // will receive 42

alts(...channels) -> Promise

The alts function will race taking values from multiple channels.

const chan1 = channel();
const chan2 = channel();
put(chan2, 42);
const msg = await alts(chan1, chan2); // will receive 42

select(Map<*, channel>|Set<channel>|Array<channel>|Object<string, channel>) -> Promise

The select function will race taking values from multiple channels, similar to alts, but will also return the key of the channel that was selected.

const chan1 = channel();
const chan2 = channel();
put(chan2, 42);
const channels = [chan1, chan2];
const result = await select(channels); // will receive [1, 42]

Works with Map and Set as well as with plain-old javascript arrays and objects.

drain(channel) -> Promise

The drain function requires a channel which it will drain all messages from until empty, returning an array of messages.

const chan = channel();
put(chan, 42);
put(chan, 41);
put(chan, 40);
put(chan, 39);
const msgs = await drain(chan); // will receive [ 42, 41, 40, 39 ]


Contributions are welcomed and appreciated!

  1. Fork this repository.
  2. Make your changes, documenting your new code with comments.
  3. Submit a pull request with a sane commit message.

Feel free to get in touch if you have any questions.


Please see the LICENSE file for more information.




npm i @paybase/csp

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