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That seems to be a logical thing to ensure has been validated before this code is run, so no need to complicate the simple example in a HN post?

> avoid all the mess that comes with trying to clone anything else than primitives types

is an odd way to suffix code that will throw a SyntaxError when handed a primitive type.

Any cloning happens on data retrieved from an API, which is always JSON, and cannot contain undefined by definition.

There's this really nifty concept called "guarding" that helps with recovering from that sort of thing.

Just chuck a check in front of it

Or NaN or Infinity.