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    1.0.5 • Public • Published


    A functional-programming-friendly library for rolling virtual dice. It provides pure-functional way to create random numbers and dice (functions that create random integers), combine and modiify the dice results, and convert strings like "2d6+2" to functions. It has no dependencies and is about 2KB minified.

    Instead of using objects, the library creates random number generators based on the parameters you provide. The library uses higher-order functions to modify the results in order to modify or multiply the results of the dice rolls. Most of the functions return a () => number (aliased in the Typescript code as NumberGenerator).

    The functions that produce random numbers, such as createDie(), typicially have two versions: one that takes a random number generator (RNG) as the first parameter and have the suffix With as in createDieWith(), the other which is already seeded with Math.random() as the RNG as in createDie()


    Create a basic die with createDie()

    // takes a number of faces for the die as an argument and returns a function that generates ints.
    const d6 = createDie(6);
    // random int between 1 and 6

    You can use any number (>=2) of faces

    const coinFlip = createDie(2);
    const devilDie = createDie(666);

    Create multiple dice with a modifier in one step using createDice()

    // takes a number of faces, number of dice (default 1), and modifier (default +0)
    // 2d6+3
    const _2d6plus3 = createDice(6, 2, 3);
    // Random result of rolling 2 six sided dice and adding 3 to the result.
    // (1..6) + (1..6) + 3
    // Note, this is not the same as a random int between 5..15.
    // Because each die gets rolled independently, the results are more likely to follow a normal distribution curve favoring the middle numbers (like 7) more than the edge numbers (like 2 and 12)
    // 2d6+0
    const _2d6 = createDice(6, 2);
    // 1d6+0
    const _1d6 = createDice(6);

    Combine multiple dice functions with combineDice()

    const d6 = createDie(6);
    const d8 = createDie(8);
    // always returns 2
    const two = () => 2;
    // 2d6+1d8+2
    const _2d6_1d8_2 = combineDice([d6, d6, d8, two]);
    // generate random int
    // (1..6) + (1..6) + (1..8) + 2

    Dice Strings

    Using parseDiceString(s) will convert a string into a function that rolls dice based on the input. The format of the string is inspired by Tabletop RPG dice notation.



    • multiplier is the number of dice (default is 1)
    • Use d or D to separate the multiplier from the number of sides on the dice.
    • sides is the number of sides on the dice. The range will be 1 to sides, inclusive.
    • modifier is an integer to add to the total


    • "d6" -> roll one 6-sided-die`
    • "2d6" -> roll two 6-sided-dice and sum results`
    • "3d6+2" -> roll three 6-sided-dice, add 2 to the sum.`
    • "2d12-2" -> roll two 12-sided-dice, subtract 2 from the sum.`
    • "1d12-5+2d20+4+d4" -> roll one 12-sided-die, two 20-sided-dice, and one 4-sided-die, subtract 5 and add 4 to the sum.`

    Whitespace and letter case are ignored.

    Custom dice with createCustomDie()

    To create a die that isn't typical, you can use createCustomDie() and provide an array of dice face values.

    // Generate a random color string
    const colors = ["red", "orange", "yellow", "green", "blue", "indigo", "violet"];
    const colorDie = createCustomDie(colors);
    colorDie(); // "blue"
    // Create a die that lands on 6 more often.
    const weightedD6 = createCustomDie([1, 2, 3, 4, 5, 6, 6, 6]);
    weightedD6(); // 6, probably
    // If the values are numerical, they can be combined with other dice functions...
    const weightedDice = combineDice([weightedDie, weightedDie]);

    Custom Random seed

    All the fuctions that rely on a random number generator come with a version that uses Math.random for the RNG. To use a different generator, use the alternate versions with the suffix With as in createDieWith(f) where f is a function that takes no arguments and returns a number, n, where 0.0<=n<1.0

    const myRNG = randomSeed.create("my seed");
    const createDieSeeded = createDieWith(myRNG);
    const d6 = createDieSeeded(6);
    d6(); // uses myRNG for generating numbers.

    Other functions

    TBD. Meanwhile, please review test folder for examples.

    Below this line is boilerplate from TSDX


    Library bootstrapped with TSDX

    For more info, see


    TSDX scaffolds your new library inside /src.

    To run TSDX, use:

    npm start # or yarn start

    This builds to /dist and runs the project in watch mode so any edits you save inside src causes a rebuild to /dist.

    To do a one-off build, use npm run build or yarn build.

    To run tests, use npm test or yarn test.


    Code quality is set up for you with prettier, husky, and lint-staged. Adjust the respective fields in package.json accordingly.


    Jest tests are set up to run with npm test or yarn test.

    You can also use yarn test --watch or yarn test --coverage

    Bundle Analysis

    size-limit is set up to calculate the real cost of your library with npm run size and visualize the bundle with npm run analyze.


    TSDX uses Rollup as a bundler and generates multiple rollup configs for various module formats and build settings. See Optimizations for details.


    tsconfig.json is set up to interpret dom and esnext types, as well as react for jsx. Adjust according to your needs.

    Continuous Integration

    GitHub Actions

    Two actions are added by default:

    • main which installs deps w/ cache, lints, tests, and builds on all pushes against a Node and OS matrix
    • size which comments cost comparison of your library on every pull request using size-limit


    Please see the main tsdx optimizations docs. In particular, know that you can take advantage of development-only optimizations:

    // ./types/index.d.ts
    declare var __DEV__: boolean;
    // inside your code...
    if (__DEV__) {

    You can also choose to install and use invariant and warning functions.

    Module Formats

    CJS, ESModules, and UMD module formats are supported.

    The appropriate paths are configured in package.json and dist/index.js accordingly. Please report if any issues are found.

    Named Exports

    Per Palmer Group guidelines, always use named exports. Code split inside your React app instead of your React library.

    Including Styles

    There are many ways to ship styles, including with CSS-in-JS. TSDX has no opinion on this, configure how you like.

    For vanilla CSS, you can include it at the root directory and add it to the files section in your package.json, so that it can be imported separately by your users and run through their bundler's loader.

    Publishing to NPM

    We recommend using np.


    npm i dicekit-fp

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