2019-07-15 Dev.to challenge

20190715.js

const when = (when = () => false, fn = i => i) => 
    (v, idx, arr) => when(v, idx, arr) 
        ? (typeof fn === "function" ? fn(v, idx, arr) : fn)
        : v;

const reverseString = str => Array.from(str).reverse().join("");

const reverseWords = ({inString = "", ofLength = 0} = {}) => 
    inString.split(" ")
        .map(when(w => w.length >= ofLength, reverseString))
        .join(" ");

const assert = (expr, msg = "Assertion failed") => {
    if (!expr) {
        throw new Error(msg);
    }
}

assert(reverseWords({inString: "", ofLength: 5}) === "");
assert(reverseWords({inString: "hi", ofLength: 5}) === "hi");
assert(reverseWords({inString: "hi you", ofLength: 5}) === "hi you");
assert(reverseWords({inString: "hi  you", ofLength: 5}) === "hi  you");
assert(reverseWords({inString: "one two three four", ofLength: 5}) === "one two eerht four");
assert(reverseWords({inString: "sixteen candles burn", ofLength: 5}) === "neetxis seldnac burn");