AI solution for JavaScript Coding Question on BFE.dev
144. serialize and deserialize data types not supported in JSON

One possible solution could be to define custom serialization and deserialization functions for each special data type:

function serialize(value) {
  if (typeof value === "bigint") {
    return { _type: "bigint", value: value.toString() };
  } else if (value != value) { // NaN check
    return { _type: "nan" };
  } else if (value === Infinity) {
    return { _type: "infinity", sign: 1 };
  } else if (value === -Infinity) {
    return { _type: "infinity", sign: -1 };
  } else { // use default JSON.stringify for other types
    return value;
  }
}

function deserialize(value) {
  if (value && typeof value === "object") {
    switch (value._type) {
      case "bigint":
        return BigInt(value.value);
      case "nan":
        return NaN;
      case "infinity":
        return value.sign * Infinity;
      default:
        return value;
    }
  } else { // use default JSON.parse for other types
    return value;
  }
}

function stringify(data) {
  return JSON.stringify(data, serialize);
}

function parse(string) {
  return JSON.parse(string, deserialize);
}

The serialize function checks for each special data type and returns an object that includes a _type field and other necessary fields for that type. For example, for BigInts it stores the string representation of the value, for NaN it simply indicates the type as "nan", and for Infinity it stores the sign as 1 or -1.

The deserialize function checks if the input value is an object with a _type field, and if so, creates a new value based on the type and the stored information. For example, for BigInts it calls the BigInt constructor with the stored string value, for NaN it returns the NaN constant, and for Infinity it multiplies the stored sign with the Infinity constant.

The stringify and parse functions simply use JSON.stringify and JSON.parse with the custom serialize and deserialize functions passed as the second argument, respectively.

Now we can test it with the examples from the prompt:

console.log(parse(stringify([1n, null, undefined, NaN]))); // [1n, null, undefined, NaN]
console.log(parse(stringify({a: undefined, b: NaN}))); // {a: undefined, b: NaN}

Both examples should output the expected results.