functional javascript w/ composition

const test = require('tape') // Forward/reverse function chain helper - See examples, way simpler in code - tldr: this glues other functions toghether function _composer(reverse = false) { // @uglytruth // Returns higher-order-function, executes using Array.reduce syntax (link mdn article). // Starting with the initial arguments, each function is sequentially executed, passing arguments from one function to the next - functions MUST RETURN THE VALUE TO HAND-OFF. // Only supports single param functions - **this is a feature** return function _directionalFunChain() { const fns = Array.from(arguments); return function _partial() { return Array.from(fns) [reverse ? 'reduceRight' : 'reduce']((last, fn) => fn && fn(last) || last, [...arguments]); }.bind(this); } } // The wrapper fn supports reverse - literally only changes the inner fn '_partial' const compose = _composer(); const composeRight = _composer(true); // Define a Pure-at-heart function (https://en.wikipedia.org/wiki/Pure_function) const add5 = n => { n = parseInt(n) + 5 return n; // required } test('sequence of 3 functions', t => { const add15 = compose(add5, add5, add5); t.equals(add15(0), 15) t.equals(add15(5), 20) t.equals(add15('5'), 20) t.end(); }) // Define some Pure-at-heart functions (https://en.wikipedia.org/wiki/Pure_function) const half = n => { n = (parseInt(n) * 0.5).toFixed(2) return n; // required } const square = n => { n = Math.pow(parseInt(n)).toFixed(2) return n; // required } test('sequence of different functions', t => { const add5HalfSquare = compose(add5, half, square); t.equals(add5HalfSquare(5), 25, 'I can caz maths?') // 5+5==10, half(10)==5, 5*5==25 t.end(); })