Newton's Method to get square root

newton.js

function sqrt_iter(g, y) {
    if (Math.abs(g*g - y) < 0.000000000000001) {
        return g;
    } else {
        return sqrt_iter( (g + y / g)/2, y ); 
    }
}
function sqrt(y) {
    return sqrt_iter(1.0, y);
}