Superjson

Requirements

• Export serialize(value) and deserialize(text) as named functions, and a default object containing both. serialize returns a string; deserialize restores a value with its original supported types. The wire format is your choice and need not match the SuperJSON package.
• Support null, strings, booleans, finite numbers, negative zero, NaN, positive/negative Infinity, undefined, BigInt, valid Date objects, RegExp source and flags, arrays, plain objects, null-prototype objects, Map keys/values, and Set entries, recursively.
• Preserve array length and holes separately from explicit undefined entries. Preserve own enumerable string object keys, including properties whose values are undefined and keys such as __proto__. Preserve Map and Set insertion order. Ignore symbol/non-enumerable object keys and extra properties on built-ins.
• Return fresh objects, arrays, dates, regular expressions, maps, and sets. Do not mutate input or call a custom toJSON method. Repeated references may be independently reconstructed; identity relationships do not need to survive. RegExp lastIndex is not preserved.
• Throw TypeError for cycles, invalid Date objects, functions, symbols, and unsupported object instances. An ancestor tracking set must allow repeated references that are not cyclic.
• Ordinary user data that resembles metadata must round-trip normally. No reserved user key may overwrite type information or change a restored object prototype. Invalid JSON throws SyntaxError. Other syntactically valid strings not produced by your serializer are outside scope.

Examples

Input: deserialize(serialize({ count: BigInt("42"), missing: undefined, at: new Date("2025-01-01T00:00:00Z") }));
Output: Restores count as 42n, an own missing property, and at as a Date.

Input: deserialize(serialize([NaN, -0, new Set([1, 2])]));
Output: Restores NaN, negative zero, and a Set in the original order.