const string = "((()())())";

function check(str) {
  let stack = [];
  for (let i=0; i < str.length; i++){
    if(str[i] == "(")
      stack.push(str[i]);
    else if(str[i] == ")") {
        if(stack.pop() != "(") { return false; }
    }
  }

  return !stack.length;
}

console.log(check(string))