Add the global structuredClone() method

[realtimetodie]

Adds the global structuredClone() method to the Window scope. The method was introduced in Node.js version 17.0.0 (release notes). The available polyfills of the structuredClone() method for Node.js are considered to be incomplete in comparison to the web browser JavaScript runtime implementations.

Example - Error message when the structuredClone() method is not defined in the global scope of Node.js (Node.js < 17)

ReferenceError: structuredClone is not defined

Users can provide their own polyfill of the structuredClone() method (Node.js < 17)

global.structuredClone = (value, options) => ...

References

• Specification: HTML Standard
• MDN: structuredClone()
• Node.js Documentation: structuredClone()

Resolves #3363

[realtimetodie]

@domenic

[domenic]

This does not implement the specification linked, or have any tests.

[realtimetodie]

Excuse me, but the structuredClone() method is a global object in the Node.js runtime, and the implementation simply reflects this method into the VM context. How does this "not implement the specification linked"?

[domenic]

Because Node's structured clone operates on Node objects, not on jsdom (web) objects.

[realtimetodie]

Alright, fair enough. So, according to the structured clone algorithm, the following JSDOM Web/API types need to be covered differently, otherwise their non-enumerable properties, property accessors, and object prototypes are not preserved and they will be cloned as plain JavaScript objects.

• Blob
• DOMException
• File
• FileList

I am looking into this and will add some tests as requested.

[domenic]

You shouldn't need to add too many tests. They should already exist in web platform tests. See CONTRIBUTING.md. The main goal here is to enable https://github.com/web-platform-tests/wpt/blob/master/html/webappapis/structured-clone/structured-clone.any.js ; if you can get that passing, the PR is probably ready.

[acywatson]

@domenic do you have any ideas on how I could move this forward? It seems like core-js has an implementation that follows the spec, AFAICT. Should we copy that code over, modifying it as necessary? It's unfortunate to have it in two places, but I'm not sure if you're interested in taking a dependency on core-js for this. Either way, I see no real reason to re-implement this from scratch in js-dom.

[domenic]

I think I gave pretty clear instructions above, about how to proceed. If you want to see someone following them, check out #3521 .

[acywatson]

I think I gave pretty clear instructions above, about how to proceed. If you want to see someone following them, check out #3521 .

I'll have to respectfully disagree - if it was clear, then I wouldn't be asking a clarifying question about it :). I think that's a reasonable thing to do before starting work on something like this.

Great to see someone else is working on this, though and I appreciate the response.