Escape from Callback Mountain v2.6.0
Functional River pattern?
What is the
It is an async & sync version of the Collection Pipeline pattern.
Your parameters/data represents the water, and functions form the riverbed.
Roughly speaking, my definition of pipeline is a sequential series of chained functions where arguments line up with return values (using Array methods, Promises, or similar). Key to my adaptaion is using named functions.
This ultimately results in your code reading like a step-by-step story.
Compare these 2 examples:
// ❌ Non-Functional River / Collection Pipeline Code ❌
const formatScores = scores => scores
.map(x => x * 2.0)
.map(x = x.toFixed(2))
// ✅ Functional River Code ✅
const formatScores = scores => scores
Let's look at a more complex example, with asynchronous requirements added in the mix...
Comparison: Callbacks vs. Functional River
See both Before and After examples below.
Node-style Callbacks w/ Nesting
Note: This is intentionally reasonable callback code. Even if nested. Not trying a straw-man attack.
'Functional River' Pattern
The technique I demonstrate hopefully illustrates the Functional River pattern:
Functional River Goals/Benefits:
- Higher level logic implemented with multiple smaller single-purpose functions, assembled to read like a story.
- Decoupled modules are easier to maintain & upgrade over time.
- Reduce bugs by relocating ad hoc logic. (e.g. one-off transformations, untested validation)
- Use same interface for both synchronous & asynchronous code. (
promise.then(value => alert(value)))
- Prefer immutable, stateless code as essential building blocks.
- Less elaborate, modular code is naturally more reusable.
- Easier to move logic around - rebundle simple functions as needed to create new higher-order functions.
- Increased testability - eliminate hidden surface area.
- Substantially faster code readability - versus artisinal functions assembled with ad hoc code glue (a Big Ball of Mud).
Have feedback, fixes or questions? Please create
If you feel this subject has already been exhauted, please see my post Beating a dead horse?
Step 1: Break Up The Big Functions - read the code: PR #2: Flatten Functions
Step 2: DRYer Code - read the code: PR #3: DRYer Code
Step 3: Cleanup Code - read the code: PR #5: Post Cleanup
Pros & Cons
- Less ad hoc code results in:
- More uniform code between different teams & developers,
- Performance tooling & refactoring is an appreciably better experience,
- More certainty about code correctness,
- Higher code reuse.
- 100% Unit Testability
- Unit tests uniquely prove you found, understand, AND resolved a given bug,
- Faster bug resolution process,
- Flatter code hierarchy == less filler to remember
- Performance. I've run some micro-benchmarks - it's not awesome. However, 3 important things:
- It's not meaningfully slower in real world applications.
- If it is necessary, performance analysis & tuning is a much improved experience. Smaller functions make it easier to see where slow code lurks - especially if you profile unit tests.
- As more people adopt these patterns, things will improve. V8/Chrome has been impressively fast at optimizing for emerging patterns.
- Debugging can be more difficult. Though I have updated my dev tricks to debug this style of code, even without the confort of Bluebird's error handling. I'll add more sample scripts for this later.
- Something new to learn. Deal with it, you're a developer.
- If you have an existing project with lots of code, the unfortunate reality is: Refactors Suck.
- EventEmitter- & Stream-based code is not improved much, if at all, using this technique. Look into RxJS
- Ongoing experiments include simple closures, extend Promise with
EventEmitter, or using Bluebird's
.bind to inject variable state into the Promise chain. (I know, "ugh side-effects, gross." PRs welcome.)
It's perhaps true that an overly-done flat & modular JS Project can feel more disorganized over time. New practices & approaches must be explored (from monorepos, to breaking up modules when-needed to meet org/dev/deployment needs).
Project and code discipline is just as important as it's always been. Also, the community is still developing consensus around Functional JS patterns, immutability and overall project organization.
When done right, one of Functional River's greatest strengths is the ability to relocate & rearrange modules with low risk. If this still feels risky, your modules are probably still too entangled (coupled).
Ultimately my goal is to better understand & advance Modular + Functional JS patterns. Hopefully I can interest some of the skeptics along the way 🤞
Please Star this project ❤️
Credits & Inspiration
I highly recommend reading (or watching) every single link here.
Escape from Callback Mountain Key Updates
- README now more focused on the Functional River pattern.
- Counter-examples are still included in
./src, just not featured on README.
- There's an updated production-ready library
Functional Promises which grew out of the feedback & research from this Project.