SOURCE

function f(str) {
    let count = 0;
    let findCount = function (str) {
        for (let i = 0; i < str.length - 1; i++) {
            if(str[i] === str[i+1]) {
                str = str.slice(0, i) + str.slice(i+2);
                count++;
                return findCount(str);
            }
        }
        return;
    }
    findCount(str);
    console.log(count);
}

f('12344321')