This is the specification as it relates to JSON: https://tc39.github.io/proposal-bigint/#sec-serializejsonproperty https://tc39.github.io/proposal-bigint/#sec-s

This is the specification as it relates to JSON: https://tc39.github.io/proposal-bigint/#sec-serializejsonproperty https://tc39.github.io/proposal-bigint/#sec-serializejsonpro... Basically, serialization will throw if there is a BigInt present. But, the .toJSON() callout is supported if a particular environment wants to opt-in to supporting it in some manner.