const countOccurrences = (text, str) => {
    let count = 0, i = -1, len = text.length - str.length;
    while (i++ <= len) count += text.startsWith(str, i)
    return count;
};
console.log(countOccurrences('ababa', 'aba'));

const countOccurrences = (text, str) => {
    let count = 0, i = 0, len = text.length - str.length;
    while (i <= len) {
    i = text.indexOf(str, i);
    if(!++i) break;
    count++;
    }
    return count;
};
console.log(countOccurrences('ababa', 'aba'));

countOccurrences('aaa', 'aa');//???