Math api polyfill

Math.trunc = Math.trunc || function(x) {
    return x < 0 ? Math.ceil(x) : Math.floor(x);
}

Math.sign = Math.sign || function(x) {
  x = +x; // convert to number
  if (x === 0 || isNaN(x)) {
    return x;
  }
  return x > 0 ? 1 : -1;
}

Math.cbrt = Math.cbrt || function(x) {
  var y = Math.pow(Math.abs(x), 1/3);
  return x < 0 ? -y : y;
}