Weighted random number generators <https://codepen.io/samme/pen/dPPRKjO>

random.js

const { asin, cos, random, PI } = Math;

// Average 0.333
const Low = () => random() ** 2;

// Average 0.666
const High = () => 1 - random() ** 2;

// Average 0.5, middle-biased
const Mid = () => 0.5 + asin(2 * random() - 1) / PI;

// Average 0.5, end-biased
const HighLow = () => 0.5 * (1 - cos(PI * random()));

// Random value within [min, max)
const Rand = (min, max, rand) => min + (max - min) * rand();

// Random array member
const Pick = (arr, rand) => arr[Math.floor(rand() * arr.length)];