Deep-copying in JavaScript using structuredClone | Hacker News Reader

Deep-copying in JavaScript using structuredClone

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21 pointsfeross11 comments

This is sorely needed and a welcome addition.

Tangent: What are they referring to when they write "The Platform" (capitalized) as in "The Platform now ships with ....".

It sounds a little too Borg-like and creepy.

The "(Open) Web Platform" perhaps? A term that numerous groups like the W3C were trying to push hard but that doesn't seem to have hugely caught on in day to day conversation.

This is very useful and definitely something I am glad to see added to the language, previous solutions to this problem weren’t particularly efficient.

I am confused why they made it a global function though rather than a static method like object.assign though

also

> Functions: If your object contains functions, they will be quiety discarded.

that is a bit of a let down

i believe thats for the hack, stringifying then parsing the object.

Oops I can’t read

I think it's true for both -- they mention this both under the "Deep copies" section where it's talking about JSON.parse(JSON.stringify()), and also under "Structured cloning" > "Features and limitations" where it's talking about the new function. The line GP quoted is from the section where it's talking about structured cloning.

Serializing functions is an exciting footgun of pain due to capturing/closures. Sure there are plenty of places where you could serialize easily, it’s super easy to become nonserializable and you end up in a position where sometime a function serializes, and sometimes it fails. Then there are semantic issues in later execution as a lot of primitive operations are defined in terms of the host global object, etc.

So the safest option is to not support serialization.

Whenever I research the performance problem of a JavaScript library, I stumble over many deep clones even when it is not necessary most of the time. People are just not aware how CPU expensive a deep clone in JavaScript is, even more on big objects.

For example when you run a Node.JS profiling on the PouchDB test suite, most CPU cycles are spend in running the clone() function.

Having an updated performance comparison of structuredClone() would be great.

I found that if I’m deep copying then that’s a sign my software design is wrong.

There’s a lot of challenges and problems with deep copying, better to find another way.

> The Platform now ships with structuredClone() ...

What's "The Platform"?

Awesome right in time

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