Behavior of Structured Clone
Structured clone is JavaScript’s algorithm to create “deep copies” of values. It is used for postMessage() and therefore is used extensively under the hood with Comlink. By default, every function parameter and function return value is structured cloned. Here is a table of how the structured clone algorithm handles different kinds of values. Or to phrase it differently: If you pass a value from the left side as a parameter into a proxy’d function, the actual function code will get what is listed on the right side.
| Input | Output | Notes |
|---|---|---|
[1,2,3] |
[1,2,3] |
Full copy |
{a: 1, b: 2} |
{a: 1, b: 2} |
Full copy |
{a: 1, b() { return 2; } |
{a: 1} |
Full copy, functions omitted |
new MyClass() |
{...} |
Just the properties |
Map |
Map |
Map is structured cloneable |
Set |
Set |
Set is structured cloneable |
ArrayBuffer |
ArrayBuffer |
ArrayBuffer is structured cloneable |
Uint32Array |
Uint32Array |
Uint32Array and all the other typed arrays are structured cloneable |
Event |
❌ | |
| Any DOM element | ❌ | |
MessagePort |
❌ | Only transferable, not structured cloneable |
Request |
❌ | |
Response |
❌ | |
ReadableStream |
❌ | Streams are planned to be transferable, but not structured cloneable |