Forever in a Do While Loop

var randomNumber = getRandomNumber(low, high);
var guess;
var guessCount = 0;
var correctGuess = false;
var low = 1;
var high = 10;

function getRandomNumber( lower, upper ) {
  var num = Math.floor(Math.random() * (upper - lower + 1)) + lower;
  return num;
}

do {
  guess = prompt('I am thinking of a number between ' + low + ' and ' + high + '. What is it?');
  guessCount += 1;
  if (parseInt(guess) === randomNumber) {
    correctGuess = true;
  }
} while ( ! correctGuess )

document.write('<h1>You guessed the number!</h1');
document.write('It took you ' + guessCount + ' tries to guess the number ' + randomNumber + '.');