const list =[ // a 班在今年的第1周打扫了3次卫生 { name :' a 班', count :3, week :1},{ name :' b 班', count :4, week :1},{ name :' c 班', count :5, week :2},{ name :' a 班', count :3, week :3},{ name :' b 班', count :4, week :3}求各班级打扫卫生的总数，在打扫卫生的周里，平均每周打扫了几次

根据给定的列表，我们可以使用 JavaScript 来计算各班级打扫卫生的总数和平均每周打扫次数。下面是相应的代码：

const list = [
  { name: 'a班', count: 3, week: 1 },
  { name: 'b班', count: 4, week: 1 },
  { name: 'c班', count: 5, week: 2 },
  { name: 'a班', count: 3, week: 3 },
  { name: 'b班', count: 4, week: 3 }
];

// 计算各班级打扫卫生的总数
const totalByClass = {};
list.forEach(item => {
  const { name, count } = item;
  if (!totalByClass[name]) {
    totalByClass[name] = 0;
  }
  totalByClass[name] += count;
});

console.log('各班级打扫卫生的总数：', totalByClass);

// 计算平均每周打扫次数
const totalByWeek = {};
const countByWeek = {};
list.forEach(item => {
  const { week, count } = item;
  if (!totalByWeek[week]) {
    totalByWeek[week] = 0;
    countByWeek[week] = 0;
  }
  totalByWeek[week] += count;
  countByWeek[week]++;
});

const averageByWeek = {};
for (const week in totalByWeek) {
  averageByWeek[week] = totalByWeek[week] / countByWeek[week];
}

console.log('平均每周打扫次数：', averageByWeek);

运行上述代码，将得到以下输出：

各班级打扫卫生的总数： { a班: 6, b班: 8, c班: 5 }
平均每周打扫次数： { '1': 3.5, '2': 5, '3': 3.5 }

这里我们使用了两个对象 `totalByClass` 和 `totalByWeek` 来分别存储各班级的总数和每周的总数。然后，通过计算每周打扫次数的总和和出现的次数，我们得到了平均每周打扫次数的结果。