`getUserList` 将发出一个数组 flowchart LR s((start)) arr["[user 1, user 2, user 3]"] e((end)) s --> arr --> e `mergeMap((users) => from(users))` 将数组中的元素依次发出 flowchart LR s((start)) user1[user 1] user2[user 2] user3[user 3] e((end)) s --> user1 --> user2 --> user3 --> e mergeMap((user) => getUserDetails(user.id).pipe(map((details) => ({ ...user, details }))) ); 为每个用户添加 details flowchart LR s((start)) user1["{ user 1, details 1 }"] user2["{ user 2, details 2 }"] user3["{ user 3, details 3 }"] e((end)) s --> user1 --> user2 --> user3 --> e