Return person first name or surName

surName.js

/**
 * Return the name and surname
 * "Tiago Gouvêa de Oliveira" will return "Tiago Gouvea"
 * @author TiagoGouvea
 * @param name
 * @returns String
 */
function nameSurname (name) {
    name = name.trim();
    if (!name) return '';
    return firstName(name) + " " + surName(name);
}

/**
 * Return the person firt name
 * @author TiagoGouvea
 * @returns String
 * @param name
 */
function firstName (name) {
    name = name.trim();
    if (!name) return '';
    let names = name.split(" ");
    if (names.length === 1) { return name; } else { return names[0]; }
}

/**
 * Return the person sur name
 * @author TiagoGouvea
 * @returns String
 * @param name
 */
function surName (name) {
    name = name.trim();
    if (!name) return '';
    let names = name.trim().split(" ");
    let sur = '';
    if (names.length >= 2) { sur = names[1]; }
    if (names.length >= 3 && (['de', 'da', 'do', 'dos', 'das', 'del', 'dal', 'das']).indexOf(sur.toLowerCase()) > -1) { sur = names[1] + " " + names[2]; }
    return sur;
}