Sends content before and after another stream

output.md

Below you will find the contents of some-file.txt:

just a file

That's all folks!

usage.js

const fs = require('fs');
const wrapStream = require('./wrap-stream');

fs.createReadStream('some-file.txt') // file contents: 'just a file'
  .pipe(wrapStream('## Below you will find the contents of some-file.txt:\n\n```\n', '\n```\n\nThat\'s all folks!')
  .pipe('output.md')
;

wrap-stream.js

function wrapStream(prefix, suffix) {
  let once = false;

  return new Transform({
    objectMode: true,
    transform(chunk, _, callback) {
      if (!once) {
        once = true;
        callback(null, `${prefix}${chunk}`);
      }
      else {
        callback(null, chunk);
      }
    },

    flush(callback) {
      callback(null, suffix);
    }
  });
}

module.exports = wrapStream;