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Rubico - [a]synchronous functional programming - Interview with Richard Tong


One of the tricky parts of JavaScript is dealing with asynchronous behavior. The language itself has introduced improved syntax (async/await) and utilities like Promise.all and Promise.race but it’s not enough for more advanced use cases.

To learn about a potential solution, I am interviewing Richard Tong about a new library called Rubico.

Can you tell a bit about yourself?

Richard Tong

I am a programmer based in Los Angeles who enjoys solving problems with JavaScript. Currently, I am working on Claimyr - the quickest way to speak with an unemployment agent. In my spare time, I enjoy going out to eat and getting coffee.

How would you describe Rubico to someone who has never heard of it?

Rubico is a set of functions that supports a simple and expressive way of programming in JavaScript. With Rubico, you can reduce a ton of boilerplate surrounding Promise handling in your code, allowing you to focus on writing business logic and shipping quickly. Rubico is geared towards ES2018+, requiring syntax for async generator functions.

How does Rubico work?

Use Rubico’s operators to create async-enabled compositions of functions. Each operator handles Promise resolution for you. Consider the following example:

const { pipe, map, filter } = rubico;

const isOdd = (number) => number % 2 == 1;

const asyncSquare = async (number) => number ** 2;

const squaredOdds = pipe([
  // each asyncSquare Promise is resolved before filter

squaredOdds([1, 2, 3, 4, 5]).then(console.log); // [1, 9, 25]

At the moment, Rubico supports the following functions:

const {
} = rubico;

You can create full applications with just pipe and tap. Usually I recommend people start with these two. Use pipe to chain a bunch of functions (sync or async) together, then use tap to specify any “side-effecting” functions, i.e., functions that shouldn’t contribute to the main flow, such as writing to a file or database. The rule is pretty arbitrary and will always be as pure as your best effort.

Here’s a setup you could get started with that I’ve been using for my HTTP handlers:

const MyHttpHandler = ({
  dependencyA, dependencyB, myConfigValue,
}) => (request, response) => tryCatch(pipe([
  transform(map(chunk => chunk), Buffer.from('')),
  callProp('toString', 'utf8'),
  // { parameterA: 'hey', parameterB: 100 }
]), error => {
  response.writeHead(error.code ?? 500, {
    'Content-Type': 'text/plain',

// Initialize dependencies, grab config values...
  dependencyA, dependencyB, myConfigValue,

If you are interested in getting started with Rubico, I recommend taking the tour and then glancing over all the functions at the docs. Try to master the core API first, then move on to the advanced functions in rubico/x.

How does Rubico differ from other solutions?

Rubico is comparable to Lodash FP, Ramda, Bluebird, and RxJS libraries. All five libraries are competing in the utility space, though with differing core principles/ideologies. I’ve compared them briefly below to show you the differences:

Rubico vs Lodash FP:

  • Lodash FP - immutable, auto-curried, iteratee-first, and data-last methods
  • Rubico - mutable, uncurried, promise-resolving, iteratee-first, and data-last methods

Rubico vs Ramda:

  • Ramda - immutability, and side-effect free functions are at the heart of its design philosophy
  • Rubico - composability, performance, and simplicity are at the heart of its design philosophy

Rubico vs Bluebird:

  • Bluebird - built around Promises. Utility operators focus on Promise handling.
  • Rubico - built around async functions. Utility operators focus on async function composition.

Rubico vs RxJS:

  • RxJS - a library for composing asynchronous and event-based programs by using observable sequences
  • Rubico - a library for composing asynchronous and event-based programs with async functions


Rubico, Lodash FP, and Ramda all have a placeholder operator __. Rubico’s __ can be used in conjunction with Rubico’s curry to create new functions from existing ones by fixing some of the arguments.

Lodash FP and Ramda don’t need the curry function as much because their functions come as auto-curried. Rubico does not curry automatically for performance reasons and instead exports higher-order functions with fixed signatures.

const { curry, __ } = require("rubico");
const R = require("ramda");
const _ = require("lodash/fp");

const add = (a, b) => a + b;

// rubico
const add3Rubico = curry(add, __, 3);
add3Rubico(5); // 8

// ramda
const add3Ramda = R.curry(add)(R.__, 3);
add3Ramda(5); // 8

// lodash/fp
const add3Lodash = _.curry(add)(_.__, 3);
add3Lodash(5); // 8

Both Rubico and Bluebird provide an asynchronous pooling option. With Rubico, you can specify an asynchronous limit while applying an async function to each item of a collection via the property function map.pool. Bluebird enables pooling functionality via the concurrency option on Bluebird’s

const Promise = require("bluebird");
const { map } = require("rubico");

const sleep = (ms) =>
  new Promise((resolve) => setTimeout(resolve, ms));

// bluebird
  [1, 2, 3, 4, 5],
  async function asyncSquare(number) {
    console.log("squaring", number);
    await sleep(500);
    return number ** 2;
  { concurrency: 2 }

// rubico
map.pool(2, async function asyncSquare(number) {
  console.log("squaring", number);
  await sleep(500);
  return number ** 2;
})([1, 2, 3, 4, 5]);

Why did you develop Rubico?

Initially, I developed Rubico because I needed a function that could chain async functions together in a data-last fashion. Then I wondered about other ways in which async functions could be composed. The rest went from there.

What next?

I’m building Claimyr with Rubico and a couple of other libraries I’m working on: Presidium and Arche.

Presidium provides a type system that addresses the complete set of needs of a back-end Node.js application architect: from handling HTTP to working with Amazon Web Services like DynamoDB or S3, to deploying on your in-house docker swarm.

Arche is a simple wrapper over React, enabling a declarative interface for working with React without the need for transpilation.

These libraries and others contribute to high-quality software development at Claimyr.

Rubico has a long roadmap - it is just getting started. There’s still a lot of cool and useful asynchronous behaviors yet to be implemented. For example, reduce.parallel could apply an asynchronous reducer in parallel to a possibly infinite or asynchronous source.

I think it’s hard to predict exactly where we’ll end up in the next few years or next year even. Innovation happens every day, for sure - chances are you’ll be using new software a year from now.

What advice would you give to programmers getting into web development?

If you feel like you are struggling, keep at it for as long as you can, then get a good night’s sleep. Chances are, you will grasp it a little better the next day.

Who should I interview next?

Thomas Wang, the co-founder of @Napkin.

Any last remarks?

Thanks for giving me the time.

It’s an exciting time to be a web developer. If you are interested in contributing to Rubico or any of my other projects, or even just learning about how to build for the web, please reach out to me via email.


Thanks for the interview, Richard! Rubico looks like a great solution for handling any complex asynchronous case and I hope you keep improving it.

You can find rubico on npm and on GitHub.