Using Taylor Series to calculate Trig Functions in JavaScript

taylorSeriesTrig.js

"use strict";

const power = (x, exp) => (exp < 1) ? 1 : x * power(x, exp - 1);
const factorial = x => (x < 1) ? 1 : x * factorial(x - 1);
const seriesTerm = (x, exp) => power(x, exp) / factorial(exp);
const zeroExpander = zeroes => zeroes < 0 ? 1 : 10 * zeroExpander(zeroes - 1);
const accuracyLimit = (seriesTerm, decimalPlaces) =>
	seriesTerm < (decimalPlaces / zeroExpander(decimalPlaces + 1));

const seriesHelper = (x, exp, add, term = seriesTerm(x, exp)) =>
	(accuracyLimit(term, 5)) ?
		0 :
		add ?
			term + seriesHelper(x, exp + 2, !add) :
			(term * -1) + seriesHelper(x, exp + 2, !add);

const sin = x => x + seriesHelper(x, 3, false);
const cos = x => 1 + seriesHelper(x, 2, false);
const tan = x => sin(x) / cos(x);
const cot = x => 1 / tan(x);

const calc = (fn, num) => console.log(`${fn.name}(${num}) = ${fn(num).toFixed(6)}`);

const num = 0.9;

calc(sin, num);
calc(cos, num);
calc(tan, num);
calc(cot, num);