Reference

Transfer vs clone

Move ownership instead of copying bytes. Companion to lesson 3. MDN: Transferable objects.

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Two calls, one idea

// Same realm — explicit clone + optional move
const copy = structuredClone(u8, { transfer: [u8.buffer] });

// Other realm — implicit clone + optional move
worker.postMessage(u8, [u8.buffer]);

The transfer list only marks how listed resources move. They must also appear in the value graph, or they detach with nowhere to land.
Typed arrays are cloneable, not transferable. Put .buffer in the list.
After transfer the source is detached (byteLength === 0). A detached buffer cannot be cloned or transferred again.

When to transfer

Hard problem	Default
Large binary; sender is done with the bytes	Transfer
Both sides still need the bytes	Clone (or copy first, then transfer one copy)
Same-realm snapshot that must freeze the original	`structuredClone(value, { transfer })` — source detaches
BroadcastChannel / IndexedDB / History	Clone only — no transfer list
Small objects, Dates, Maps, DTOs	Clone; transfer is the wrong tool

Common transferables

ArrayBuffer, MessagePort, ImageBitmap, OffscreenCanvas, ReadableStream / WritableStream / TransformStream, VideoFrame, AudioData. Marked [Transferable] in Web IDL. Do not memorize the long tail — check MDN when a type is unfamiliar.