Yeah there are plenty of JS libraries for large numbers, but all of them are a bit of a hack. They are not as fast as native compiler/interpreter support, and there is no obvious way to integrate the logic into other native functions such as JSON.parse and JSON.stringify. So you have to create your own JSON parser which is not as fast like I did: https://github.com/datalanche/json-bignum
That is fine if the JSON consumer and producer are Javascript. What happens when the producer is a language that handles large numbers correctly? The numbers are rounded in Javascript.