JS solutions

unbalanced-parentheses.js

/**
Can be tested quickly with Javasript REPL extension for VS Code
*//

function test_string(str) {

  var par_count = 0;
  for (var i = 0; i < str.length; i++) {
    if (str[i] == '(') par_count++;
    else if (str[i] == ')') par_count--;

    if (par_count < 0) {
      console.log(`Unbalanced at char ${par_count}, unexpected closing ")"`);
      return false;
    }
  }

  if (par_count > 0) {
    console.log('Not closed "("');
    return false;
  }

  return true;

}

test_string('((('); //= false
test_string(''); //= true
test_string("((())))))))");//= false
test_string('(())');//= true