Awesome

Fortuna

The quick solution for everything random!

A Gacha-like system to roll random items with weights.

Usage

More weight = more common. Think of it as in terms of probability.

// Deno
import { GachaMachine } from "https://deno.land/x/fortuna/mod.ts"
// JSR
import { GachaMachine } from "jsr:@nekooftheabyss/fortuna@4.1.3"
// Node
import { GachaMachine } from "@nekooftheabyss/fortuna"
// esm.sh
import { GachaMachine } from "https://esm.sh/jsr/@nekooftheabyss/fortuna@4.1.3"

const items = [
    { result: "SSR cool character", chance: 1 },
    { result: "Kinda rare character", chance: 3 },
    { result: "Mob character #1", chance: 5 },
    { result: "Mob character #2", chance: 5 },
    { result: "Mob character #3", chance: 5 },
]

const machine = new GachaMachine(items)

machine.get(10) // Rolls 10x

/*
    My result:
    [
      "Kinda rare character",
      "Mob character #1",
      "Mob character #3",
      "Mob character #3",
      "Mob character #1",
      "Kinda rare character",
      "Mob character #2",
      "Mob character #2" ,
      "Mob character #1",
      "Mob character #2"
    ]
*/

Rolling distinct elements

You can roll distinct elements using the LimitedGachaMachine. It is slower than GachaMachine but there shouldn't be much noticeable difference.

The "distinct" behavior only applies to within a single .get() call. It doesn't affect the pool of items used when initializing new LimitedGachaMachine().

import { LimitedGachaMachine } from "https://deno.land/x/fortuna/mod.ts"
// JSR
import { LimitedGachaMachine } from "jsr:@nekooftheabyss/fortuna@4.1.3"

const items = [
    { result: "SSR cool character", chance: 1 },
    { result: "Kinda rare character", chance: 3 },
    { result: "Mob character #1", chance: 5 },
    { result: "Mob character #2", chance: 5 },
    { result: "Mob character #3", chance: 5 },
]

const machine = new LimitedGachaMachine(items)

machine.get(4) // Rolls 4x

/*
    My result:
    [
      "Kinda rare character",
      "Mob character #1",
      "Mob character #3",
      "Mob character #2",
    ]
*/

Plain weighted random selection

You probably don't need all complicated stuff. Here's a quick way to just create a simple weight-based gacha system: (Only works on v3.0.1 and above)

import { roll } from "jsr:@nekooftheabyss/fortuna@4.1.3/roll"; // wherever you are importing from.

const items = [
    { result: "SSR cool character", chance: 1 },
    { result: "Kinda rare character", chance: 3 },
    { result: "Mob character #1", chance: 5 },
    { result: "Mob character #2", chance: 5 },
    { result: "Mob character #3", chance: 5 },
];

roll(items); // Rolls one item from the list of items using linear search.

You can also provide two individual arrays for choices and weights.

import { roll } from "jsr:@nekooftheabyss/fortuna@4.1.3/roll"; // wherever you are importing from.

const items = [
    "SSR cool character",
    "Kinda rare character",
    "Mob character #1",
    "Mob character #2",
    "Mob character #3",
];
const chances = [1, 3, 5, 5, 5];

roll(items, chances); // Rolls one item from the list of items using linear search.

Providing the total chance may result in faster rolls.

import { roll } from "jsr:@nekooftheabyss/fortuna@4.1.3/roll"; // wherever you are importing from.

const items = [
    { result: "SSR cool character", chance: 1 },
    { result: "Kinda rare character", chance: 3 },
    { result: "Mob character #1", chance: 5 },
    { result: "Mob character #2", chance: 5 },
    { result: "Mob character #3", chance: 5 },
];

roll(items, 19); // Rolls one item from the list of items using linear search.

import { roll } from "jsr:@nekooftheabyss/fortuna@4.1.3/roll"; // wherever you are importing from.

const items = [
    "SSR cool character",
    "Kinda rare character",
    "Mob character #1",
    "Mob character #2",
    "Mob character #3",
];
const chances = [1, 3, 5, 5, 5];

roll(items, chances, 19); // Rolls one item from the list of items using linear search.

Documentation

Documentation for the latest version can be found in jsr:@nekooftheabyss/fortuna