function findLongestWord(string) {
    if (typeof string !== 'string' || string.trim().length === 0) {
        return '';
    }

    return string.trim().split(/\s+/).reduce((maxWord, word) => {
        return word.length > maxWord.length ? word : maxWord;
    }, '');
}

let longestWord = findLongestWord(" abc def ghiiii axiiii ");
console.log(longestWord); // Output: "ghiiii"