28 lines
3.4 KiB
Markdown
28 lines
3.4 KiB
Markdown
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# Behavior of [Structured Clone]
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[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.
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| Input | Output | Notes |
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| -------------------------- | :------------: | -------------------------------------------------------------------------------------------- |
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| `[1,2,3]` | `[1,2,3]` | Full copy |
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| `{a: 1, b: 2}` | `{a: 1, b: 2}` | Full copy |
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| `{a: 1, b() { return 2; }` | `{a: 1}` | Full copy, functions omitted |
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| `new MyClass()` | `{...}` | Just the properties |
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| `Map` | `Map` | [`Map`][map] is structured cloneable |
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| `Set` | `Set` | [`Set`][set] is structured cloneable |
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| `ArrayBuffer` | `ArrayBuffer` | [`ArrayBuffer`][arraybuffer] is structured cloneable |
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| `Uint32Array` | `Uint32Array` | [`Uint32Array`][uint32array] and all the other typed arrays are structured cloneable |
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| `Event` | ❌ | |
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| Any DOM element | ❌ | |
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| `MessagePort` | ❌ | Only transferable, not structured cloneable |
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| `Request` | ❌ | |
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| `Response` | ❌ | |
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| `ReadableStream` | ❌ | [Streams are planned to be transferable][transferable streams], but not structured cloneable |
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[structured clone]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm
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[map]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map
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[set]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set
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[arraybuffer]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer
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[uint32array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint32Array
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[transferable streams]: https://github.com/whatwg/streams/blob/master/transferable-streams-explainer.md
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