How about augmenting the built-in Array object to use Math.max/Math.min instead:

Array.prototype.max = function() {
  return Math.max.apply(null, this);
};

Array.prototype.min = function() {
  return Math.min.apply(null, this);
};

let p = [35,2,65,7,8,9,12,121,33,99];

console.log(`Max value is: ${p.max()}` +
  `\nMin value is: ${p.min()}`);

Here is a JSFiddle.

Augmenting the built-ins can cause collisions with other libraries (some see), so you may be more comfortable with just apply'ing Math.xxx() to your array directly:

var min = Math.min.apply(null, arr),
    max = Math.max.apply(null, arr);

Alternately, assuming your browser supports ECMAScript 6, you can use spread syntax which functions similarly to the apply method:

var min = Math.min( ...arr ),
    max = Math.max( ...arr );