Basic implementation of the Newton’s Method for narrowing in on a square root. NOTE: in Firefox the yield keyword doesn’t exist unless the script tag loading the function has a type of “text/javascript;version=1.7”. version must be 1.7 or higher.

function newton(value, guess) {
   value = Math.abs(value);
   guess = Math.abs(guess);
   while (1) {
      guess = guess - (((guess * guess) - value) / (2 * guess));
      yield guess;
   }
}

var g = newton(83521, 190);
for (var i = 0; i < 10; i++) {
    document.write(g.next() + "<br />");
}