我需要将subject和entity作为一个组合键，然后再按日期从小到大排序，生成新的

如果需要将subject和entity作为一个组合键，可以在比较函数中将两个属性组合起来进行比较，代码如下：

const data = [
  { subject: "Math", entity: "A", date: "2021-01-01" },
  { subject: "Math", entity: "A", date: "2021-02-01" },
  { subject: "Science", entity: "A", date: "2021-03-01" },
  { subject: "Science", entity: "A", date: "2021-01-15" }
];

data.sort((a, b) => {
  const keyA = a.subject + a.entity;
  const keyB = b.subject + b.entity;
  if (keyA !== keyB) {
    return keyA.localeCompare(keyB);
  } else {
    return new Date(a.date) - new Date(b.date);
  }
});

console.log(data);

输出结果为：

[
  { subject: 'Math', entity: 'A', date: '2021-01-01' },
  { subject: 'Math', entity: 'A', date: '2021-02-01' },
  { subject: 'Science', entity: 'A', date: '2021-01-15' },
  { subject: 'Science', entity: 'A', date: '2021-03-01' }
]

可以看到，数据已经按照subject和entity组合键，再按日期依次排序。