Packing

Some layers only pass along an error’s message (or cause) and throw away every other property. Certain RPC systems do this, and so do job queues and the boundary into a Cloudflare Durable Object. Packing tucks the whole error into one of the fields that do survive, so you can rebuild it on the other side.

Packing

import { EErrorPackType } from "@nice-code/error";

// `pack` MUTATES the error in place — it rewrites the chosen field (message/cause) on
// THIS instance and returns the same object (not a clone). The original value is stashed
// internally so `unpack` can restore it.
error.pack(EErrorPackType.msg_pack);   // embeds the JSON into error.message
error.pack(EErrorPackType.cause_pack); // embeds the JSON into error.cause

Throw the packed error across the boundary like any normal Error.

Unpacking

error.unpack(); // restore the original NiceError

You rarely call unpack yourself. castNiceError notices a packed error and unpacks it for you:

import { castNiceError } from "@nice-code/error";

const restored = castNiceError(caught); // unpacks if it was packed

When to reach for it

• A Durable Object only re-throws message when you call into it. Pack with msg_pack before throwing inside the DO.
• A job queue only keeps the error’s message. Pack before adding the job, then castNiceError after pulling it off.
• Any layer where you don’t control how things are serialized and only the standard Error fields make it through.

For boundaries you do control, such as your own HTTP responses, use toJsonObject() + castNiceError instead. Packing is only for the ones you don’t.