Discover functional programming patterns with RamdaJS. Learn about pure functions, currying, and point-free style while deepening your knowledge of map, filter, and reduce methods.

We know the functional programming (FP) hype train's been riding strong the past few years, especially in the JavaScript community. We extol FP in countless books, videos, and blog posts, with no sign of slowing down.

As a result this course isn't to convince you, today's JS developer, of how awesome FP is. I'm simply sharing some popular patterns using Ramda, an FP library that I've blogged on many times.

Before going through them, though, we will lay the groundwork with concepts like pure functions, currying, and point-free style.

You're already doing FP through map, filter, reduce, and Lodash, so why not dive a bit deeper and see if you like it down here?

Functional Programming Patterns With RamdaJS!

Since `score` is an array of numbers, we know `map`'s involved. It lets us loop and transform each score as we see fit.

What would we do with each score? Let's review the challenge.

* At or above 800, return “{score} is excellent!”
* At or above 700, return “{score} is good”
* At or above 650, return “{score} is fair”
* At or below 649, return “{score} is poor”

Imperatively, that sounds like a bunch of `if/else` statements.

Luckily though, Ramda has us covered. `cond` can easily replace this logic with functions!

import { cond } from 'ramda';

const reviewCreditScore = cond([
  [(score) => score >= 800, (score) => `${score} is excellent!`],
  [(score) => score >= 700, (score) => `${score} is good`],
  [(score) => score >= 650, (score) => `${score} is fair`],
  [(score) => score <= 649, (score) => `${score} is poor`]
]);

console.log(reviewCreditScore(800));


It does look a bit confusing with all the arrows, however.

If you'd like to make the comparisons point-free, try `gte` and `lte`.

import { cond, gte, lte } from 'ramda';

const reviewCreditScore = cond([
  [lte(800), (score) => `${score} is excellent!`],
  [lte(700), (score) => `${score} is good`],
  [lte(650), (score) => `${score} is fair`],
  [gte(649), (score) => `${score} is poor`]
]);

console.log(reviewCreditScore(800));


Now compose it with `map` to review all the scores!

import { cond, gte, lte, map } from 'ramda';
import scores from './scores.json';

const reviewCreditScore = cond([
  [lte(800), (score) => `${score} is excellent!`],
  [lte(700), (score) => `${score} is good`],
  [lte(650), (score) => `${score} is fair`],
  [gte(649), (score) => `${score} is poor`]
]);

const reviewCreditScores = map(reviewCreditScore);

console.log(reviewCreditScores(scores));


Introduction

Pure Functions

Higher-Order Functions

Function Composition

Currying

Pipe and Compose

Sorting

Conditional Logic

Using What We've Learned

Functors

Lenses

Lenses Exercises

Building a Wikipedia Search

Closing Comments

Rating Credit Scores: Solution Review