Reduce: the power of a higher-order function

reduce_is_powerful.js

/*
    A quick demo of the power of the `reduce()` higher-order function.

    In this demo, `reduce()` has been used to replicate several of its
    higher-order cousins: `map()`, `filter()`, and `find()`. The point is
    to show that `reduce()` is a functional multi-tool. If you have
    `reduce()``, you're on your way to some functional bliss.

    For each example, the native version of the higher-order function is
    shown before the reduce version. The native versions are much more
    concise, of course. The point is to show that they're not _required_,
    even though they're _preferred_.

    This example makes use of a couple of ES6/ES2015 features, namely arrow
    functions and `let`. Therefore, you'll want to use something like babel
    or the latest (4.x+) versions of node.js if you try this out.
 */
'use strict';

let arr = [
    {
        name: "Fred",
        age: 43,
        species: "human"
    },
    {
        name: "Mary",
        age: 48,
        species: "human"
    },
    {
        name: "Cal",
        age: 9,
        species: "human"
    },
    {
        name: "Purrf",
        age: 10,
        species: "cat"
    },
    {
        name: "Toots",
        age: 2,
        species: "dog"
    }
];



// var humans = arr.filter((member) => member.species === "human");
// reduce as filter
let humans = arr.reduce(function(sum, member){
    if (member.species === "human") {
        sum.push(member);
    }
    return sum;
}, []);
console.log(humans);


// var names = arr.map((member) => member.name);
// reduce as map
let names = arr.reduce(function(sum, member) {
    sum.push(member.name);
    return sum;
}, []);
console.log(names);

// var firstDog = arr.find((member) => member.species === "dog");
// reduce as find
let firstDog = arr.reduce(function(sum, member) {
    if (!sum && member.species === "dog") {
        sum = member;
    }
    return sum;
}, undefined);
console.log(firstDog);