odd-occurrences

function solve2(str) {
    str = str.split(' ')
        .map(x => x.toLowerCase());

    const wordCounter = {};

    // initialize the wordCounter
    for (const el of Array.from(new Set([...str]))) {
        wordCounter[el] = 0;
    }

    // populate the wordCounter
    for (const word of str) {
        if (wordCounter.hasOwnProperty(word)) {
            wordCounter[word]++;
        }
    }

    // sort and print
    const countOdd = [...Object.entries(wordCounter)].filter(([k, v]) => v % 2 === 1); // [[c#, 3], ...]
    console.log(countOdd.map(e => e[0]).join(' '));
}