在 node 中如何判断一个对象是 stream
Issue 欢迎在 Gtihub Issue 中回答此问题: Issue 357
Author 回答者: shfshanyue
stream 可以通过缓冲区来高效利用内存，从而提高性能。常用场景如读写大文件、http-server 中的大静态文件渲染。
每一个 stream 都有 pipe 函数，可以用来判断一个对象是否 stream。
代码如下，摘自 is-stream: 一个周下载量两千万的 npm package。
const isStream = (stream) =>
stream !== null &&
typeof stream === "object" &&
typeof stream.pipe === "function";
isStream.writable = (stream) =>
isStream(stream) &&
stream.writable !== false &&
typeof stream._write === "function" &&
typeof stream._writableState === "object";
isStream.readable = (stream) =>
isStream(stream) &&
stream.readable !== false &&
typeof stream._read === "function" &&
typeof stream._readableState === "object";
isStream.duplex = (stream) =>
isStream.writable(stream) && isStream.readable(stream);
isStream.transform = (stream) =>
isStream.duplex(stream) &&
typeof stream._transform === "function" &&
typeof stream._transformState === "object";鸭子判断？