Trying to add a conditional to a function, and receiving an error on execution

Question

So, first and foremost, it's important to note that I'm adding a feature to something I didn't design. I'm really new to JavaScript, and I'm trying to edit an existing Discord bot. I discovered that the simplest way to achieve my goal would be to edit the root function at which it generates Random numbers. The relavant snippet of the original code (taken from the dice-expression-evaluator module https://github.com/dbkang/dice-expression-evaluator) is as follows:

Dice.prototype.roll = function () {
     var rolls = [];
     var sum = 0;
     for (var i = 0; i < this.diceCount; i++) {
          var roll = random.integer(1, this.sideCount) * this.coefficient;
          rolls.push(roll);
          sum += roll;
     }
     return {roll: sum, dice: rolls};
};

This original code works just fine, but doesn't include my desired feature (a simple-but-verbose sort of whitelist.) the 4 variables not defined in that particular code block are rather self-explanatory. My version of the code (slightly edited for privacy reasons) is as follows:

Dice.prototype.roll = function () {
  var rolls = [];
  var sum = 0;
  var range = this.whitelist(); //already tried it with () after whitelist
  console.log(range.join(','));
  for (var i = 0; i < this.diceCount; i++) {
    var roll = random.integer(range[0], range[1]) * this.coefficient; //changed the 2 function arguments, but both are still integers
    rolls.push(roll);
    sum += roll;
  }
  return {roll: sum, dice: rolls};
};

Dice.prototype.whitelist = function () {
  let user0 = "a";
  let user1 = "b";
  let user2 = "c";
  let user3 = "d";

  let user = message.author.id;
  let die = this.sideCount;
  console.log(user);
  console.log(string(die));
  if (user==user0) {
    var min = Math.ceil(0.76 * die);
    var max = die;
  } else if (user==user1) {
    var min = Math.ceil(0.76 * die);
    var max = die;
  } else if (user==user2) {
    var min = 1;
    var max = die;
  } else if (user==user3) {
    var min = 1;
    var max = die;
  } else {
    var min = 1;
    var max = die;
  }
  return [min, max];
};

The message.author.id variable is available to the function that started the whole function chain 3 scopes up, but in MY version of the code, (even after correcting a few missing semicolons and similarly minute errors) a dice expression that is perfectly functional in the original code generates an "invalid dice expression" error. Other than the introduction of a new variable and the variables in the random.integer call, I see no functional difference between the old and new versions of Dice.prototype.roll. By my understanding, my whitelist function returns an array of integers, and those integers are being injected directly into the random.integer function call in a perfectly reasonable way... I am incredibly confused.