ES2018 Dice Roller

README.md

Roll

Roll any number of dice on your command line, including modifiers!

Dependencies

Requrise node v8.x or higher.

Usage

$ node index.js roll1 [, roll2, ..., rollN]

Format your rolls as [integer]d[size][+ or -][modifier], such as 1d20+4 or 2d6-1.

Assuming you alias roll to node index.js:

$ roll 1d20+6 2d6+4 1d6-1 1d4
11 = 1d20 (5) + 6
6 = 1d6 (1) + 1d6 (1) + 4
2 = 1d6 (3) + -1
1 = 1d4 (1) + 0

index.js

// Utilities
const times = n => Array.from({ length: n }).map(n => n + 1);
const compact = [(acc, x) => x ? [...acc, x] : acc, []];
const sum = [(acc, n) => acc + n, 0];
const randBetween = (lower, upper) => Math.floor(Math.random() * (upper - lower + 1) + lower);

// Parsing
const parseInput = die => die.replace(/\s/g, '').match(/(\d*)d(\d+)(?:([\+-])(\d+))?/);
const operators = {
  '+': str => parseInt(str, 10),
  '-': str => -1 * parseInt(str, 10),
};
const toNumber = (operator, modifier) => operators[operator] ? operators[operator](modifier) : 0;

// Dice
const rollDie = size => randBetween(1, size);
const generateDiceRolls = ([str, count, size, operator, modifier]) => ({
  count,
  size,
  rolls: times(count).map(() => rollDie(size)),
  modifier: toNumber(operator, modifier),
});
const total = roll => roll.rolls.reduce(...sum) + roll.modifier;

// Display
const individuals = roll => times(roll.count)
  .map((n, i) => `1d${roll.size} (${roll.rolls[i]})`)
  .join(' + ');
const formatRoll = roll => `${total(roll)} = ${individuals(roll)} + ${roll.modifier}`;

// Application
const [, , ...dice] = process.argv;
const rolls = dice
  .map(parseInput)
  .reduce(...compact)
  .map(generateDiceRolls)
  .map(formatRoll);

rolls.forEach(roll => console.log(roll));

package.json

{
  "name": "roll",
  "version": "1.0.0",
  "description": "Roll arbitrary dice on the command line",
  "main": "index.js",
  "repository": "https://github.com/Kerrick/roll",
  "author": "Kerrick Long <me@kerricklong.com>",
  "license": "MIT"
}