What is getReadableStreamSomehow()?

Question

Node.js

The book has an example:

let fs = require("fs");

let stream = fs.createReadStream("file.txt"); // ~400kb
let readable = getReadableStreamSomehow();

stream.on("data", chunk => {
  console.log(`got ${chunk.length} bytes of data`);

  stream.pause();

  console.log("There will be no more data for 10 second");

  setTimeout(() => {
    console.log("Now data will start again");

    stream.resume();
  }, 10000);
})

But an error occurs that getReadableStreamSomehow is not found. The documentation also uses this function in some examples. Where is she from and why? What is it all about. The example declares a readable variable but doesn't use it...