docs: function elastic(amplitude, period) {
    if ( amplitude === void 0 ) amplitude = 1;
    if ( period === void 0 ) period = .5;
  
    var a = minMax(amplitude, 1, 10);
    var p = minMax(period, .1, 2);
    return function (t) {
      return (t === 0 || t === 1) ? t : 
        -a * Math.pow(2, 10 * (t - 1)) * Math.sin((((t - 1) - (p / (Math.PI * 2) * Math.asin(1 / a))) * (Math.PI * 2)) / p);
    }
  }