Stream is readable

Checks if the given argument is a readable stream.

• Check if the value is different from null.
• Use typeof to check if the value is of type object and the pipe property is of type function.
• Additionally check if the typeof the _read and _readableState properties are function and object respectively.

const isReadableStream = val =>
  val !== null &&
  typeof val === 'object' &&
  typeof val.pipe === 'function' &&
  typeof val._read === 'function' &&
  typeof val._readableState === 'object';

const fs = require('fs');

isReadableStream(fs.createReadStream('test.txt')); // true