How to test if an object is a Stream in NodeJS

Question

I have a function which receives an object that could be a string, Buffer or Stream.

I can easily test if the object is a Buffer like so: if (x instanceof Buffer)

What's the best way to test if an object is a Stream? There doesn't appear to be a Stream base class in node - is there?

What should I look for?

Answer 1

For Readable you can do:

var stream = require('stream');  function isReadableStream(obj) {   return obj instanceof stream.Stream &&     typeof (obj._read === 'function') &&     typeof (obj._readableState === 'object'); }  console.log(isReadableStream(fs.createReadStream('car.jpg'))); // true console.log(isReadableStream({}))); // false console.log(isReadableStream(''))); // false 

Answer 2

Not all streams are implemented using stream.Readable and stream.Writable.

process.stdout instanceof require("stream").Writable; // false process.stdout instanceof require("readable-stream").Writable; // false 

The better method is to individually check for the read(), write(), end() functions.

var EventEmitter = require("events");  function isReadableStream(test) {     return test instanceof EventEmitter && typeof test.read === 'function' }  function isWritableStream(test) {     return test instanceof EventEmitter && typeof test.write === 'function' && typeof test.end === 'function' } 

You can always reffer to: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/node/node.d.ts#L252