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 );

According to MDN Math.min accepts only numbers, and if one of the arguments is not a number, it'll return NaN.

That's not what it says (bold emphasis mine):

If at least one of arguments cannot be converted to a number, the result is NaN.

Type Conversion:

• Math.min uses ToNumber to convert its arguments.
• ToNumber uses ToPrimitive to convert Objects (and Arrays are Objects).
• ToPrimitive uses toString
• [5].toString() is '5', which gets returned to ToPrimitive, which returns it to ToNumber, which parses it to 5 and returns it to Math.min, for which it is a valid argument, because it is not NaN.
• [1, 2].toString(), OTOH, is '1, 2', which gets returned to ToPrimitive, which returns it to ToNumber, which parses it to NaN, because it is not a valid number representation. ToNumber then passes NaN to Math.min, which will then return NaN, because (as MDN states it) "one of its arguments cannot be converted to a number" or (as the spec states it) "If any value is NaN, the result is NaN.".