es6_functional_javascript_example.js

const { map, filter, reduce } = require('lodash');


// array from 0 to 9
const data = [0,1,2,3,4,5,6,7,8,9];

// helper functions
const doubled   = val => val * 2;
const isEven    = val => val % 2;
const isOverTen = val => val >= 10;

// multi-variable helper function
const totaled = (total, n) => total + n;

// functional
const mapped   = data.map(doubled);  // 0,2,4,6,8,10,12,14,16,18
const filtered = data.filter(isEven);  // 1,3,5,7,9
const reduced  = data.reduce(totaled);  // 45

// chained functional calls
const map_filter_reduce = data.map(doubled)
                              .filter(isOverTen)
                              .reduce(totaled);  // 75

// output
console.log(`mapped: ${mapped}`);  // mapped: 0,2,4,6,8,10,12,14,16,18
console.log(`filtered: ${filtered}`);  // filtered: 1,3,5,7,9
console.log(`reduced: ${reduced}`);  // reduced: 45
console.log(`map_filter_reduce: ${map_filter_reduce}`);  // map_filter_reduce: 70