compose

/*
    compose(fn1, fn2, fn3, ...)(1)
*/

const fn1 = function(val) { console.log(val, '+ 1 = ', val + 1); return val + 1 };
const fn2 = function(val) { console.log(val, '+ 2 = ', val + 2); return val + 2 };
const fn3 = function(val) { console.log(val, '+ 3 = ', val + 3); return val + 3 };
const fn4 = function(val) { console.log(val, '+ 4 = ', val + 4); return val + 4 };

// ES6
const compose1 = (...fns) => val => fns.reduce((arg, fn) => fn(arg), val);

// ES5
var compose = function() {
    var fns = arguments;
    return function(val) {
        var res = val;

        for (var i = 0; i < fns.length; i++) {
            res = fns[i](res)
        }

        return res;
    }
}