Number.prototype.squared = function() { return this * this }
Array.prototype.last = function() { return this[this.length - 1] }

x = 2
guess = 1

step = function() {
  return guess = (guess + x / guess) / 2
}

guesses = []
do { guesses.push(step()) } while (Math.abs(x - guesses.last().squared()) > 0.0000000001)
guesses