Depends on the type of large data, but since 2011 there's "Transferable" [1], where objects like ArrayBuffer, MessagePort, and ImageBitmap can be transferred with a low overhead [2]. Now, if you're passing large arbitrary object graphs, you're out of luck.

[1] https://developers.google.com/web/updates/2011/12/Transferab... [2] https://developer.mozilla.org/en-US/docs/Web/API/Worker/post...