Hacker News Reader

Comment by qcoret | Hacker News Reader

All Temporal objects are easily (de)serializable, though. `.toString` and `Temporal.from` work great.

That's not what I mean. Even though it is serializable, it's still not the same when you serialize/deserialize it.

For example `JSON.parse(JSON.stringify(Temporal.PlainYearMonth.from({year:2026,month:1}))).subtract({ years: 1})` won't work, because it misses the prototype and is no longer an instance of Temporal.PlainYearMonth.

This is problematic if you use tRPC for example.

Would a plain data object be an instance of PlainYearMonth?

If not, that regardless of being plain data or a serialized object with functions, you'd still need to convert it to the type you want.

You would need to use the `reviver` parameter of `JSON.parse()` to revive your date strings to Temporal objects. As others have said, it's a simple `Temporal.from()`

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

I've been doing this for so long and never knew there was a reviver param, thanks - that is super useful.

Having to provide a complete schema of your json everywhere your json gets parsed negates the advantages of json.

The main advantage of json is that it’s human readable and writable. Beyond that, it has no notion of user created data types so anyone using it has to do custom unmarshalling to get a type apart from sting, number, dict and list.

Most JSON libraries in typed languages require this for data binding to complex types though.

Which is why many developers only use JavaScript Object Notation for JavaScript objects, and only JavaScript objects that can losslessly be written as JSON. Which this proposal explicitly does not support.

{"$temporal_type":"PlainYearMonth","$data":"........"}

Even if you don't explicitly provide a schema, you implicitly still have one. The recipient needs to know what you're sending them. Unless maybe you want to start parsing JSON payloads with an LLM.

Depending on your needs (i.e. how you would otherwise use your output jspn), using the reviver can have a significant impact on performance. JSON.parse itself is hyper-optimized. At the company I work we used the reviver for almost exactly this, but profiling showed that using the reviver had enormous impact on performance. We cut it out, and won in the seconds of performance for some large json's.

Instead of using the reviver you can deserialize as a plain string, then later reassign the property as the type you want. E.g.:

  const myObject = JSON.parse(text);
  myObject.date = new Date(myObject.date);

> For example `JSON.parse(JSON.stringify(Temporal.PlainYearMonth.from({year:2026,month:1}))).subtract({ years: 1})` won't work, because it misses the prototype and is no longer an instance of Temporal.PlainYearMonth.

I don't know if I'm missing something, but that's exactly how I'd expect it to compose. Does the following do what you wanted your snippet to do?

  Temporal.PlainYearMonth.from(JSON.parse(JSON.stringify(Temporal.PlainYearMonth.from({year:2026,month:1}))))

JSON.stringify and JSON.parse should not be viewed as strict inverses of each other. `JSON.parse(JSON.stringify(x)) = x` is only true for a for a small category of values. That category is even smaller if parsing is happening in a different place than stringification because JSON doesn't specify runtime characteristics. This can lead to things like JSON parsing incorrect in JS because they're too large for JS to represent as a number.

This is also true of JavaScript Date instances, so I’m curious what solution you had that did work with raw JSON stringify and parse.

This seems more to do with how JSON works than Temporal. There are libraries such as Devalue which will handle this for you

`devalue.parse(devalue.stringify(Temporal.PlainYearMonth.from({year:2026,month:1}))).subtract({ years: 1})`

https://www.npmjs.com/package/devalue

Then you're talking about changing JSON.parse to start parsing some schema as a type instead of object, which would break compatibility.

The JSON types are string, number, boolean, null, object and array. So how could the suggested code possibly work? Do you want JSON.parse to do arbitrary code execution like Python's pickle?

Reply on news.ycombinator.com