code: function ReadableByteStreamControllerClose(controller) {
    const stream = controller._controlledReadableStream;
  
    assert(controller._closeRequested === false);
    assert(stream._state === 'readable');
  
    if (controller._totalQueuedBytes > 0) {
      controller._closeRequested = true;
  
      return;
    }
  
    if (controller._pendingPullIntos.length > 0) {
      const firstPendingPullInto = controller._pendingPullIntos[0];
      if (firstPendingPullInto.bytesFilled > 0) {
        const e = new TypeError('Insufficient bytes to fill elements in the given buffer');
        ReadableByteStreamControllerError(controller, e);
  
        throw e;
      }
    }
  
    ReadableStreamClose(stream);
  }
docs: A client of ReadableByteStreamController may use these functions directly to bypass state check.