Dev.To 2019 Aug 6 Challenge

20190806.js

const TRANSFORMER = {
    LOWER: String.prototype.toLowerCase,
    UPPER: String.prototype.toUpperCase
};

const transform = (v, which) => which.apply(v);

const weirdCase = str => 
 str.split(" ")
    .map((part) => Array.from(part)
                        .map((ch, idx) => transform(ch, idx & 1 ? TRANSFORMER.LOWER 
                                                                : TRANSFORMER.UPPER ))
                        .join(""))
    .join(" ");

const assert = (exprFn, expected, msg) => {
    const actual = exprFn();
    if (actual !== expected) {
        throw new Error(`${msg}; got ${actual}; expected ${expected}`);
    }
}

assert(() => weirdCase(""), "", "Empty");
assert(() => weirdCase("     "), "     ", "Spaces");
assert(() => weirdCase("HELLO"), "HeLlO", "All Caps");
assert(() => weirdCase("hello"), "HeLlO", "All lower case");
assert(() => weirdCase("HellO"), "HeLlO", "Mixed case");
assert(() => weirdCase("Weird string case"), "WeIrD StRiNg CaSe", "Test Case");