chained.js

/**
 * https://www.codewars.com/kata/54ca3e777120b56cb6000710
 *
 *
 Description:

 Your task is to write a higher order function for chaining together a list of unary functions. In other words, it should return a function that does a left fold on the given functions.

 chained([a,b,c,d])(input)

 Should yield the same result as

 d(c(b(a(input))))


 */

var tests = require('./lib/framework.js');
var Test = tests.Test, describe = tests.describe, it = tests.it, before = tests.before, after = tests.after;

function chained(functions) {
    return function (x) {
        return functions.reduce(function (curry, f) {
            return f(curry);
        }, x);
    }
}

function f1(x) {
    return x * 2
}
function f2(x) {
    return x + 2
}
function f3(x) {
    return Math.pow(x, 2)
}

function f4(x) {
    return x.split("").concat().reverse().join("").split(" ")
}
function f5(xs) {
    return xs.concat().reverse()
}
function f6(xs) {
    return xs.join("_")
}

Test.assertEquals(chained([f1, f2, f3])(0), 4);
Test.assertEquals(chained([f1, f2, f3])(2), 36);
Test.assertEquals(chained([f3, f2, f1])(2), 12);

Test.assertEquals(chained([f4, f5, f6])("lorem ipsum"), "merol_muspi");