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javascript/snippets/is-duplex-stream.md

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+---
+title: Stream is duplex
+type: snippet
+tags: [node,type]
+cover: digital-nomad-11
+dateModified: 2020-10-20T23:02:01+03:00
+---
+
+Checks if the given argument is a duplex (readable and writable) stream.
+
+- Check if the value is different from `null`.
+- Use `typeof` to check if a value is of type `object` and the `pipe` property is of type `function`.
+- Additionally check if the `typeof` the `_read`, `_write` and `_readableState`, `_writableState` properties are `function` and `object` respectively.
+
+```js
+const isDuplexStream = val =>
+  val !== null &&
+  typeof val === 'object' &&
+  typeof val.pipe === 'function' &&
+  typeof val._read === 'function' &&
+  typeof val._readableState === 'object' &&
+  typeof val._write === 'function' &&
+  typeof val._writableState === 'object';
+```
+
+```js
+const Stream = require('stream');
+
+isDuplexStream(new Stream.Duplex()); // true
+```