freestyle-sample.js

/* The API 
================== */
const noop = () => { };

// abstract matcher
const match = (field = '', delegate = noop) => {
  return (data = []) => {
    return data.filter(entry => delegate(entry[field]));
  }
};

// concrete matchers
const is = (target) => (value) => value === target;
const isOver = (target) => (value) => value > target;
const isUnder = (target) => (value) => value < target;
const isOrOver = (target) => (value) => value >= target;
const isOrUnder = (target) => (value) => value <= target;
const isMultipleOf = (target) => (value) => value % target === 0;

// abstract compute 
const compute = (delegate = noop, field = '') => {
  return (data) => delegate(data, field);
};

// concrete compute
const sumOf = (data = [], field = '') => {
  return data.reduce((sum, entry) => {
    return sum += entry[field] || 0;
  }, 0);
};

const averageOf = (data = [], field = '') => {
  return data.reduce((sum = 0, entry, index) => {
    sum += (entry[field] || 0);
    if (index === data.length - 1) return sum / data.length;
    return sum;
  });
};

const chain = (...fns) => {
  return (data) => {
    return fns.reduce((computed, fn) => {
      return fn(computed);
    }, data);
  };
};

/* Client Code (what you will write to use the API) 
===================================================== */
const handleData = (developers = []) => {
  const isFemale = match('gender', is('Female'));
  const isYoungAdult = match('age', isOrOver(20));
  const canPlayNightOwl = match('age', isUnder(50));
  const ageIsSpecialNumber = match('age', isMultipleOf(3));
  const sortByAgeDescending = (data = []) => {
    return data.slice().sort((a, b) => {
      return b.age - a.age;
    });
  }
  const getSpecialFemaleDevs = chain(
    isFemale,
    isYoungAdult,
    canPlayNightOwl,
    ageIsSpecialNumber,
    sortByAgeDescending
  );
  const specialFemales = getSpecialFemaleDevs(developers);
  console.log(`special females => ${specialFemales.length} entries.`);
  
  const [oldest] = specialFemales;
  const lastEntryIndex = specialFemales.length - 1;
  const {[lastEntryIndex]: youngest} = specialFemales;
  console.log(oldest, youngest);
}

const takeOff = async () => {
  try {
    const API = 'https://my.api.mockaroo.com/ssa-developers.json?key=18865cd0';
    const response = await fetch(API);
    const developers = await response.json();
    console.log(`Got ${developers.length} entries`);
    handleData(developers);
  } catch (error) {
    console.warn(error);
  }
};

takeOff();