Poker Hand Evaluation Example

#!/usr/bin/env node

// Test Hand

var hand = [
  { rank: 10, suit: 1 },
  { rank: 11, suit: 1 },
  { rank: 12, suit: 1 },
  { rank: 13, suit: 1 },
  { rank: 14, suit: 1 }
];

// Histogram
// { rank : count }

var histogram = hand.reduce( ( histogram, card ) => {
  histogram[ card.rank ] = ( histogram[ card.rank ] || 0 ) + 1;
  return histogram;
}, {} );

// Scored Histogram
// (descending by count)
// [ [ rank, count ] ]

var scoredHistogram =
  Object
    .keys( histogram )
    .map( rank => [ parseInt( rank ), histogram[ rank ] ] )
    .sort( ( a, b ) => a[ 1 ] == b[ 1 ] ? a[ 0 ] < b[ 0 ] : a[ 1 ] < b[ 1 ] );

// Suits
// [ suit : count ]

var suits = hand.reduce( ( suits, card ) => {
  suits[ card.suit ]++;
  return suits;
}, [ 0, 0, 0, 0 ] );

// Ranked Hand
// (descending by rank)
// [ index : rank ]

var rankedHand = hand.map( card => card.rank ).sort( ( a, b ) => a - b );

// Scoring

var isFlush = suits.indexOf( 5 ) >= 0;
var isWheel = rankedHand[ 4 ] === 14 && rankedHand[ 0 ] === 2;
var isStraight = (
  rankedHand[ 4 ] - rankedHand[ 3 ] === 1 || isWheel 
) && (
  rankedHand[ 3 ] - rankedHand[ 2 ] === 1 &&
  rankedHand[ 2 ] - rankedHand[ 1 ] === 1 &&
  rankedHand[ 1 ] - rankedHand[ 0 ] === 1 
);

console.log(
  isStraight && isFlush && rankedHand[ 4 ] === 14 && !isWheel ?        'Royal Flush'
: isStraight && isFlush ?                                              `Straight Flush ${ isWheel ? '( Wheel )' : '' }`
: scoredHistogram[ 0 ][ 1 ] === 4 ?                                    'Four of a Kind'
: scoredHistogram[ 0 ][ 1 ] === 3 && scoredHistogram[ 1 ][ 1 ] === 2 ? 'Full House'
: isFlush ?                                                            'Flush'
: isStraight ?                                                         `Straight ${ isWheel ? '( Wheel )' : '' }`
: scoredHistogram[ 0 ][ 1 ] === 3 && scoredHistogram[ 1 ][ 1 ] === 1 ? 'Three of a Kind'
: scoredHistogram[ 0 ][ 1 ] === 2 && scoredHistogram[ 1 ][ 1 ] === 2 ? 'Two Pair'
: scoredHistogram[ 0 ][ 1 ] === 2 && scoredHistogram[ 1 ][ 1 ] === 1 ? 'Pair'
:                                                                      `High Card ( ${ scoredHistogram[ 0 ][ 0 ] } )`
);

This is a quick implementation of:
http://nsayer.blogspot.com/2007/07/algorithm-for-evaluating-poker-hands.html