Array.prototype.sort()

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort

  function buildDeck() {
    game.deck = [];
    for (let i = 0; i < suits.length; i++) {
      for (let j = 0; j < ranks.length; j++) {
        let card = {};
        let tempValue = isNaN(ranks[j]) ? 10 : ranks[j];
        tempValue = (ranks[j] == "A") ? 11 : tempValue;
        card.suit = suits[i];
        card.rank = ranks[j];
        card.value = tempValue;
        //console.log(suits[i],ranks[j],tempValue);
        game.deck.push(card);
      }
    }
    shuffle(game.deck);
    console.log(game.deck);
  }

  function shuffle(cards) {
    cards.sort(function () {
      return .5 - Math.random();
    })
    return cards;
  }