• Version: v12.4.0
• Platform: Darwin hostname.local 18.6.0 Darwin Kernel Version 18.6.0: Thu Apr 25 23:16:27 PDT 2019; root:xnu-4903.261.4~2/RELEASE_X86_64 x86_64
• Subsystem: Stream

The async iterator functionality relies on a private API on destroy that accepts a second argument which is a callback. See here:

  return() {
    // destroy(err, cb) is a private API.
    // We can guarantee we have that here, because we control the
    // Readable class this is attached to.
    return new Promise((resolve, reject) => {
      this[kStream].destroy(null, (err) => {
        if (err) {
          reject(err);
          return;
        }
        resolve(createIterResult(undefined, true));
      });
    });
  }

This private API is not present on objects derived from Readable that have _destroy overridden. This means that premature exit from a for await loop which triggers the above return method will cause the program to end after running out of async continuations, as the callback is never called.