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!

So a given employee's JSON is shaped like this

Keeling Group

Devante

"interests": {
  "foods": {
    "sweets": {
      "iceCream": {
        "favoriteFlavor": "White Chocolate Raspberry Truffle"
      }
    }
  }
}

That's quite a few levels to go through, so Ramda's `path` function is a good start.

import { path } from 'ramda';
import data from './data.json';

const getFlavor = path([
  'interests',
  'foods',
  'sweets',
  'iceCream',
  'favoriteFlavor'
]);

const result = getFlavor(data);

console.log({ result });


Our solution must use lenses, so this can easily become a `lensPath` and `view` combination.

import { lensPath, view } from 'ramda';
import data from './data.json';

const favoriteFlavor = lensPath([
  'interests',
  'foods',
  'sweets',
  'iceCream',
  'favoriteFlavor'
]);

const result = view(favoriteFlavor, data);

console.log({ result });


But this only works for one person! Using it on a list of people returns `undefined` because your using `view` on the array.

Lela

Brian

Danielle

Jamar

Renee

Henderson

Torrey

Eliza

Alice

Janick

Jared

Anderson

Merritt

Jany

Coby

Jada

Corrine

Asia

Haven

Jackie

Minerva

Esteban

Joanny

Doyle

Ahmad

Howell

Friedrich

Makenna

Rosendo

Adolfo

Erich

Neil

Fredy

Elissa

import { lensPath, view } from 'ramda';
import employees from './employees.json';

const favoriteFlavor = lensPath([
  'interests',
  'foods',
  'sweets',
  'iceCream',
  'favoriteFlavor'
]);

const result = view(favoriteFlavor, employees);

console.log({ result });


How do we generalize a solution to a _list_?

# Map

import { lensPath, map, view } from 'ramda';
import employees from './employees.json';

const favoriteFlavor = lensPath([
  'interests',
  'foods',
  'sweets',
  'iceCream',
  'favoriteFlavor'
]);

const result = map(view(favoriteFlavor), employees);

console.log({ result });


As we previously discussed, lenses use `map` themselves. When they receive the data, they begin unfolding and traverse the data structure.

Adding `map` on top of that just loops through `employees` and feeds each one to `view` as data.

Our result is an array of everyone's favorite flavor!

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

Get the Flavors: Solution Review