# 在 node 中如何判断一个对象是 stream
Issue
欢迎在 Issue 中交流与讨论: Issue 357 (opens new window)
Author
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 (opens new window): 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';