gistfile1.js

function squareGuessFactory(x) {
  var guess=1;

  return function() {
    guess -= (guess*guess-x) / (2*guess);
    return guess;
  };
};

function newton_square_root(x, e) {
  var square_guess = squareGuessFactory(x);

  while (true) {
    var guess = square_guess();
    if (Math.abs(x - guess*guess) <= e)
      return guess;
  };
}