index.js

/**
 * Define strategies here
 */

let rnd = (deck, enemyDeck) => {
  //plays a random card
  return deck[Math.floor(Math.random() * deck.length)];
};

let lowest = (deck, enemyDeck) => {
  //plays the lowest card in own deck
  return deck.sort((a, b) => a - b)[0];
};

class Game {
  constructor(s1, s2, gameLength) {
    this.s1 = s1;
    this.s2 = s2;
    this.gameLength = gameLength;
    this.reset();
  }
  reset() {
    this.score = { 1: 0, 2: 0 };
    this.bonus = 0;
    this.decks = {
      1: Array.from(Array(this.gameLength), (x, index) => index + 1),
      2: Array.from(Array(this.gameLength), (x, index) => index + 1)
    };
  }
  runGame() {
    this.reset();
    for (let i = 0; i < this.gameLength; i++) {
      this.runRound();
    }

    if (this.score[1] > this.score[2]) {
      return 1;
    }
    if (this.score[1] < this.score[2]) {
      return 2;
    }
    return 0;
  }

  runRound() {
    let cards = {
      1: this.s1(this.decks[1], this.decks[2]),
      2: this.s2(this.decks[2], this.decks[1])
    };

    //filter cards form decks.
    this.decks[1] = this.decks[1].filter(c => c !== cards[1]);
    this.decks[2] = this.decks[2].filter(c => c !== cards[2]);
    if (cards[1] > cards[2]) {
      //p1 wins.
      this.score[1] += 1;
      this.score[1] += this.bonus;
      this.bonus = 0;
    }
    if (cards[1] < cards[2]) {
      this.score[2] += 1;
      this.score[2] += this.bonus;
      this.bonus = 0;
    }
    if (cards[1] == cards[2]) {
      //increment bonus.
      this.bonus++;
    }
  }
}

let globScore = { 0: 0, 1: 0, 2: 0 };
let gameCount = 100000000;
let updateEvery = 1000;
let cardsInHand = 11;

console.clear();
//Use strategies here
let g = new Game(rnd, lowest, cardsInHand);
for (let i = 0; i < gameCount; i++) {
  let t = g.runGame();
  globScore[t]++;
  if ((i + 1) % updateEvery == 0) {
    console.clear();
    console.log(globScore);
    console.log("After " + (i + 1) + " games");
    console.log("Player 1 wins " + (globScore[1] / (i + 1)) * 100 + "%");
    console.log("Player 2 wins " + (globScore[2] / (i + 1)) * 100 + "%");
  }
}
console.clear();
console.log(globScore);
console.log("After " + gameCount + " games");
console.log("Player 1 wins " + (globScore[1] / gameCount) * 100 + "%");
console.log("Player 2 wins " + (globScore[2] / gameCount) * 100 + "%");