This proposal adds an object with a "source" property that is passed as the 3rd argument to the reviver function in JSON.parse. This property contains the raw source text for the value being parsed. It is designed to address the issue that JSON parsing is lossy, e.g. around BigInt values. For example, `JSON.parse(" 9999999999999999", (key, val, {source}) => BigInt(source))`.
Explainers: https://github.com/tc39/proposal-json-parse-with-source/blob/master/README.md