A simple seedable PRNG

random.js

// Constants from glibc (GCC), with a period of 2**31
const M = (2 ** 31);
const A = 1103515245;
const C = 12345;
const randomSeed = (max) => Math.floor((crypto.getRandomValues(new Uint8Array(1))[0] / 255) * (max - 1));
/** Linear congruential generator */
class PRNG {
  constructor(seed = randomSeed(M)) {
    this.state = seed;
  }

  /** integer in range [0, 2**31) */
  int() {
    this.state = (Math.imul(A, this.state) + C) & (M - 1);
    return this.state;
  }

  /** float in range [0, 1] */
  float() {
    return this.int() / (M - 1);
  }

  /** integer in range [start, end) */
  range(start, end) {
    return Math.floor(this.float() * (end - start) + start)
  }
}