IMHO, the easiest way to generate a random number in a [min..max]
range with window.crypto.getRandomValues()
is described here.
An ECMAScript 2015-syntax code, in case the link is TL;TR:
function getRandomIntInclusive(min, max) {
const randomBuffer = new Uint32Array(1);
window.crypto.getRandomValues(randomBuffer);
let randomNumber = randomBuffer[0] / (0xffffffff + 1);
min = Math.ceil(min);
max = Math.floor(max);
return Math.floor(randomNumber * (max - min + 1)) + min;
}