Gulp: Flush function with through2 in gulp?

[zellwk]

Is there a way to add a file into the gulp stream with through2's flush function? I tried the following, but I got an error:

gulp.task('chapters', function () {
  return gulp.src('chapters/*.md')
    .pipe(hello())
    .pipe(gulp.dest('chapters/'))
})

function hello () {
  return through.obj(function (file, enc, cb) {
    this.push(file)
    cb()
  }, (flush) => {
    var json = new gutil.File({
      base: __dirname,
      cwd: __dirname,
      path: path.join(__dirname, 'chapters.json')
    })

    json.contents = new Buffer(JSON.stringify({test: 'test'}))

    this.push(json)
    flush()
  })
}

The error is

/Users/zellwk/Projects/private-repos/rt/gulpfile.js:59
    this.push(json)
         ^

TypeError: this.push is not a function
    at DestroyableTransform._flush (/Users/zellwk/Projects/private-repos/rt/gulpfile.js:59:10)
    at DestroyableTransform.<anonymous> (/Users/zellwk/Projects/private-repos/rt/node_modules/through2/node_modules/readable-stream/lib/_stream_transform.js:115:49)
    at DestroyableTransform.g (events.js:273:16)
    at emitNone (events.js:80:13)
    at DestroyableTransform.emit (events.js:179:7)
    at prefinish (/Users/zellwk/Projects/private-repos/rt/node_modules/through2/node_modules/readable-stream/lib/_stream_writable.js:465:12)
    at finishMaybe (/Users/zellwk/Projects/private-repos/rt/node_modules/through2/node_modules/readable-stream/lib/_stream_writable.js:473:7)
    at endWritable (/Users/zellwk/Projects/private-repos/rt/node_modules/through2/node_modules/readable-stream/lib/_stream_writable.js:485:3)
    at DestroyableTransform.Writable.end (/Users/zellwk/Projects/private-repos/rt/node_modules/through2/node_modules/readable-stream/lib/_stream_writable.js:455:41)
    at DestroyableTransform.onend (/Users/zellwk/Projects/private-repos/rt/node_modules/vinyl-fs/node_modules/readable-stream/lib/_stream_readable.js:523:10)

Apparently, this.push is undefined in the flush function. However, through2's documentation clearly states that this is possible. Any workarounds?

[contra]

You're using an arrow function which changes what this means

[phated]

Although it seems this has already been answered, support questions should be directed to StackOverflow.

[zellwk]

oh! Okay thanks