dice

dice.js

function random(min, max) { // min and max included 
  return Math.random() * (max - min + 1) + min;
}

const bet = 1
const rtp = 0.99
const max = 100

function roll(threshold, under) {
   const dice = random(0, max)
   const win = under ? dice < threshold : dice >= threshold
   const chance = under ? threshold / max : 1 - (threshold / max)
   const mul = rtp / chance
   const winAmount = win ? mul * bet : 0

  return {
    threshold,
    dice,
    win,
    chance,
    mul,
    winAmount
  } 
}

console.log(roll(2, false))