未处理的拒绝.every（...）不是函数

Question

我在做出“未处理的拒绝（TypeError）：slot.every（...）不是函数”时遇到以下错误，我似乎无法解决。

componentWillMount() {
  axios.get(API_BASE + `api/retrieveSlots`).then(response => {
    console.log("response via db: ", response.data);
    this.handleDBReponse(response.data);
  });
}

for (let day in schedule) {
  let slots = schedule[day];
  if (slots.length) slots.every(slot => slot === true)(schedule[day] = true)
}