omikuji.js

const fortuneMap = {
  [Symbol("daikichi")]: 5,
  [Symbol("chuukichi")]: 10,
  [Symbol("syoukichi")]: 20,
  [Symbol("kichi")]: 30,
  [Symbol("suekichi")]: 20,
  [Symbol("kyou")]: 10,
  [Symbol("daikyou")]: 5,
};

const randomFortune = () => {
  const omikuji = Reflect.ownKeys(fortuneMap).reduce(
    ({ range, get, ...rest }, key) => ({
      key,
      range: (range ?? 0) + fortuneMap[key],
      *get(num) {
        num <= range && get ? yield* get(num) : yield key;
      },
      ...rest,
    }),
    {
      random() {
        return this.get(Math.floor(Math.random() * this.range) + 1)
          .next()
          .value.toString()
          .slice(7, -1);
      },
    }
  );
  this.target.src = `images/omikuji_${omikuji.random()}.png`;
};