我似乎是浏览器特有的行为-Firefox会立即显示数据("Hello:")，而chrome似乎会缓冲并等待响应结束.请注意，如果您一开始写入更多数据(例如，我写了1000个"Hello")，chrome也会立即显示数据.

I seems to be browser specific behavior -- firefox shows the data ("Hello:") immediately while chrome seems to buffer and wait until the response is ended. Note that chrome also shows the data immediately if you write more data at first (e.g. I wrote 1000 "Hello"s).