27-lowball-evaluator

2-7 Lowball Hand Evaluator

A JavaScript poker hand evaluator for 2-7 (Deuce-to-Seven) Lowball variants including Triple Draw and Single Draw.

Features

• Correctly handles aces as high (not low like A-5 lowball)
• Straights and flushes count against you (as per 2-7 rules)
• Identifies special hands: Number One (7-5-4-3-2), Number Two, etc.
• Compare hands and find winners
• Zero dependencies

Installation

npm install 27-lowball-evaluator

Usage

Evaluate a Single Hand

const { LowballHand } = require('27-lowball-evaluator');

const hand = LowballHand.solve(['7h', '5c', '4d', '3s', '2h']);

console.log(hand.descr);      // "7-5-4-3-2 (Number One)"
console.log(hand.name);       // "Seven Low"
console.log(hand.handTypeName); // "High Card"
console.log(hand.rank);       // Lower is better

Compare Two Hands

const { LowballHand } = require('27-lowball-evaluator');

// Returns: -1 if first wins, 1 if second wins, 0 if tie
const result = LowballHand.compare(
  ['7h', '5c', '4d', '3s', '2h'],  // Number One
  ['8h', '6c', '4d', '3s', '2h']   // 8-low
);
console.log(result); // -1 (first hand wins)

Find Winner(s) from Multiple Hands

const { LowballHand } = require('27-lowball-evaluator');

const hands = [
  LowballHand.solve(['7h', '5c', '4d', '3s', '2h']),
  LowballHand.solve(['8h', '6c', '4d', '3s', '2h']),
  LowballHand.solve(['9h', '7c', '5d', '3s', '2h']),
];

const winners = LowballHand.winners(hands);
console.log(winners[0].descr); // "7-5-4-3-2 (Number One)"

Instance Methods

const hand1 = LowballHand.solve(['7h', '5c', '4d', '3s', '2h']);
const hand2 = LowballHand.solve(['8h', '6c', '4d', '3s', '2h']);

hand1.beats(hand2);    // true
hand1.ties(hand2);     // false
hand1.compareTo(hand2); // negative (hand1 is better)

Card Format

Cards are represented as strings: rank + suit

• Ranks: 2, 3, 4, 5, 6, 7, 8, 9, T (or 10), J, Q, K, A
• Suits: h (hearts), d (diamonds), c (clubs), s (spades)

Examples: '7h', 'As', 'Td', '2c'

2-7 Lowball Rules

In 2-7 (Deuce-to-Seven) Lowball:

1. Aces are always HIGH - A-2-3-4-5 is NOT a straight, it's A-high
2. Straights count against you - 6-5-4-3-2 is a straight (bad)
3. Flushes count against you - All same suit is bad
4. Best possible hand: 7-5-4-3-2 unsuited (called "Number One" or "the wheel")

Hand Rankings (Best to Worst)

1. High Card (no pair, no straight, no flush) - BEST
2. One Pair
3. Two Pair
4. Three of a Kind
5. Straight
6. Flush
7. Full House
8. Four of a Kind
9. Straight Flush - WORST

Top 10 Hands

1. 7-5-4-3-2 (Number One)
2. 7-6-4-3-2 (Number Two)
3. 7-6-5-3-2 (Number Three)
4. 7-6-5-4-2 (Number Four)
5. 8-5-4-3-2
6. 8-6-4-3-2
7. 8-6-5-3-2
8. 8-6-5-4-2
9. 8-6-5-4-3
10. 8-7-4-3-2

API Reference

LowballHand.solve(cards)

Create and evaluate a hand from an array of 5 card strings.

LowballHand.compare(cards1, cards2)

Compare two hands. Returns -1 if first wins, 1 if second wins, 0 for tie.

LowballHand.winners(hands)

Find winner(s) from an array of LowballHand instances. Returns array (can have multiple for ties).

Instance Properties

• hand.rank - Numeric rank (lower is better)
• hand.handType - Hand type constant (HIGH_CARD, ONE_PAIR, etc.)
• hand.handTypeName - Human-readable type ("High Card", "One Pair", etc.)
• hand.name - Short name ("Seven Low", "One Pair")
• hand.descr - Detailed description ("7-5-4-3-2 (Number One)")
• hand.cards - Original card array
• hand.sortedRanks - Ranks sorted high to low

License

MIT