BackendTask.Random

Takes an elm/random Random.Generator and runs it using a randomly generated initial seed.

type alias Data =
    { randomData : ( Int, Float )
    }

data : BackendTask FatalError Data
data =
    BackendTask.map Data
        (BackendTask.Random.generate generator)

generator : Random.Generator ( Int, Float )
generator =
    Random.map2 Tuple.pair (Random.int 0 100) (Random.float 0 100)

The random initial seed is generated using https://developer.mozilla.org/en-US/docs/Web/API/Crypto/getRandomValues to generate a single 32-bit Integer. That 32-bit Integer is then used with Random.initialSeed to create an Elm Random.Seed value. Then that Seed used to run the Generator.

Note that this is different than elm/random's Random.generate. This difference shouldn't be problematic, and in fact the BackendTask random seed generation is more cryptographically independent because you can't determine the random seed based solely on the time at which it is run. Each time you call BackendTask.generate it uses a newly generated random seed to run the Random.Generator that is passed in. In contrast, elm/random's Random.generate generates an initial seed using Time.now, and then continues with that same seed using using Random.step to get new random values after that. You can see the implementation here. However, elm/random is still not suitable in general for cryptographic uses of random because it uses 32-bits for when it steps through new seeds while running a single Random.Generator.

Gives a random 32-bit Int. This can be useful if you want to do low-level things with a cryptographically sound random 32-bit integer.

The value comes from running this code in Node using https://developer.mozilla.org/en-US/docs/Web/API/Crypto/getRandomValues:

import * as crypto from "node:crypto";

crypto.getRandomValues(new Uint32Array(1))[0]