Stream is readable
JavaScript, Node, Type · Oct 20, 2020

Checks if the given argument is a readable stream.
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