fixup: more simplify

lib/_stream_transform.js

@@ -234,46 +234,23 @@ function done(stream, er, data) {
 }
 
 const from = require('internal/streams/from');
-const createReadableStreamAsyncIterator = require('internal/streams/async_iterator');
 
 Transform.by = function by(asyncGeneratorFn, opts) {
-  let resume = null;
-  function next() {
-    if (resume) {
-      const doResume = resume;
-      resume = null;
-      doResume();
+  let _resolve;
+  let _promise = new Promise((resolve) => _resolve = resolve);
+  return from(Duplex, asyncGeneratorFn(async function*() {
+    while (true) {
+      const { chunk, done, cb } = await _promise;
+      if (done) return cb();
+      yield chunk;
+      _promise = new Promise((resolve) => _resolve = resolve);
+      cb();
     }
-  }
-  const input = new Readable({
-    objectMode: true,
-    autoDestroy: true,
-    read: next,
-    highWaterMark: 1, // TODO: Buffer here?
-    destroy (err, callback) {
-      next();
-      callback(err);
-    }
-  });
-
-  const iterator = createReadableStreamAsyncIterator(input);
-  return from(Duplex, asyncGeneratorFn(iterator), {
+  }()), {
     objectMode: true,
     autoDestroy: true,
     ...opts,
-    write(chunk, encoding, callback) {
-      if (!input.push(chunk)) {
-        resume = callback;
-      } else {
-        callback();
-      }
-    },
-    final(callback) {
-      input.push(null);
-      resume = callback;
-    },
-    destroy(err, callback) {
-      input.destroy(err, callback);
-    }
+    write: (chunk, encoding, cb) => _resolve({ chunk, done: false, cb }),
+    final: (cb) => _resolve({ done: true, cb })
   });
 };