'undefined' not considered JSON serializable?

[dBianchii]

• I have read this article: https://liveblocks.io/docs/platform/troubleshooting#lson-constraint-and-interfaces

Hi, I have a specifc type for my chess game that I need to convert from a normal useState() to a liveblocks storage state. The type I need to store is this:

type Piece = {
  id: keyof typeof pieceIds;
};
type Board = (Piece | undefined)[][];
//     ^  This I need!!!

When I try to use it, I am doing something like this:

As you can see, when I use it with null there are no errors. However, when I try to set it to undefined, it says it doesn't meet the constraint for a Lson.

I thought that undefined was JSON serializable. What's going on? Do I really need to convert my type to null? I don't want that....

[nvie]

Unfortunately, JavaScript does not allow undefined values to be serialized in JSON arrays. An array like [undefined] would become [null] on the other end, due to the fact that JSON.parse(JSON.stringify([undefined]) returns [null]. This is unfortunately out of our control. We therefore decided to not allow undefined values as list members, because this implicit conversion could take people by surprise.

Hope that helps to explain it.