FunctionalProgramming/JavaScript/6-mapping.js at master · HowProgrammingWorks/FunctionalProgramming · GitHub

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'use strict';

// Higher-Order Functions & Point-Free Style

// Map object instead of key iteration

// Imperative: Manual iteration, mutation, imperative transformation

const marcus1 = {

firstName: 'Marcus',

middleName: 'Aurelius',

lastName: 'Antoninus',

};

const marcus2 = {};

for (const key in marcus1) {

const prop = key.toLowerCase().replace('name', '');

const value = marcus1[key].toUpperCase();

marcus2[prop] = value;

}

console.log(marcus2);

// Functional: Higher-order functions, immutability, composition

const inst = (prev, prop, val) => ({ ...prev, [prop]: val });

const omap = (obj, fn) =>

Object.keys(obj).reduce((prev, key) => inst(prev, ...fn(key, obj[key])), {});

const marcus3 = {

firstName: 'Marcus',

middleName: 'Aurelius',

lastName: 'Antoninus',

};

const marcus4 = omap(marcus3, (key, val) => [

key.toLowerCase().replace('name', ''),

val.toUpperCase(),

]);

console.log(marcus4);

// Enhanced: Point-free style with function composition

const transformKey = (key) => key.toLowerCase().replace('name', '');

const transformValue = (val) => val.toUpperCase();

const transformEntry = (key, val) => [transformKey(key), transformValue(val)];

const marcus5 = omap(marcus3, transformEntry);

console.log(marcus5);

// Function composition for reusable transformations

const pipe =

(...fns) =>

(x) =>

fns.reduce((acc, fn) => fn(acc), x);

const objToUpper = (obj) => omap(obj, (key, val) => [key, val.toUpperCase()]);

const objKeysToLower = (obj) =>

omap(obj, (key, val) => [key.toLowerCase().replace('name', ''), val]);

const transformPerson = pipe(objToUpper, objKeysToLower);

console.log(transformPerson(marcus3));

FunctionalProgramming/JavaScript/6-mapping.js at master · HowProgrammingWorks/FunctionalProgramming · GitHub

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