Poker hand classification and comparison

poker.js

// [{suit:1,val:2}] -> 2 of diamonds

function isFlush(a) {
  let suit, result = true;
  for(var i=0; i<a.length;i++){ //should use a forloop to break early
    const card = a[i]
    if(suit===undefined) {
      suit = card.suit
    }else if(suit !== card.suit){
      return false
    }
  })

  return true;
}

function isStraight(a) {
  let cur = a[0].val
  for(var i=1;i<a.length;i++) {
      if(a[i].val !== cur+1) {
        return false;
      }
      cur = a[i].val;
      //cur ++;
  }
  return true
}

function isStraightFlush(a) {
  return isFlush(a) && isStraight(a)
}

function isRoyalFlush(a) {
  const is10 = a[0].val === 10
  return is10(a) && isFlush(a)
}

function isFourOfAKind(a) {
  return isNOfAKind(a,4)
}

function isThreeOfAKind(a) {
  return isNOfAKind(a,3)
}

function isNOfAKind(a,n) {
  let counts = {}
  a.forEach((card) => {
    if(counts[card.val] === undefined) {
      counts[card.val] = 1;
    }else{
      counts[card.val]++
    }
  })

  const vals = Object.values(counts)

  for(var i = 0; i< vals.length; i++) {

    if(vals[i] === n) {
      return true
    }
  }

  return false
}

function isFullHouse(a) {
  return isNOfAKind(a,3) && isNOfAKind(a,2)
}

function numberOfPairs(a) {
  let counts = {}
  a.forEach((card) => {
    if(counts[card.val] === undefined) {
      counts[card.val] = 1;
    }else{
      counts[card.val]++
    }
  })


  const vals = Object.values(counts)

  const pairs = 0;
  for(var i = 0; i< vals.length; i++) {

    if(vals[i] === 2) {
      pairs++
    }
  }

  return pairs
}

function isTwoPair(a) {
  return numberOfPairs(a) === 2;
}

function isOnePair(a) {
  return numberOfPairs(a) === 1;
}


function isHighCard(a) {
  return true;
}

const classifications = [
  isRoyalFlush,
  isStraightFlush,
  isFourOfAKind,
  isFullHouse,
  isFlush,
  isStraight,
  isThreeOfAKind,
  isTwoPair,
  isOnePair,
  isHighCard
]


function compareHands(a,b) {
  const aS = scoreHand(a), bS= scoreHand(b);
  if (aS === bS) {
    return undefined
  }else if(aS < bS) {
    return a
  }else{
    return b
  }
}

function scoreHand(a) {
  for(var i=0;i<classifications.length;i++) {
    if(classifications[i](a)) {
      return i;
    }
  }
}