From 9f67bfa82335d818d44902d334ad1a46431e9bad Mon Sep 17 00:00:00 2001
From: Yarchik <spoko.dev@gmail.com>
Date: Thu, 9 Jul 2026 12:36:10 +0100
Subject: [PATCH] fix: preserve error subtype through serialize
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`typeOf` derived the serialized error `name` from
`Object.prototype.toString`, whose tag is `Error` for every native error
subtype, so `TypeError`, `RangeError`, `SyntaxError`, `ReferenceError`,
`EvalError` and `URIError` all serialized as `{name: "Error"}` and revived
as a plain `Error`:

    deserialize(serialize(new TypeError('x'))) instanceof TypeError; // false

Native `structuredClone` keeps the subtype, and the deserializer already
rebuilds the right constructor when handed the correct name.

Use the instance `name` when it is one of the standard error names,
otherwise `Error` — matching `structuredClone`, which also normalizes
custom and aggregate errors to `Error`.
---
 cjs/deserialize.js |  2 +-
 cjs/serialize.js   |  4 ++--
 esm/deserialize.js |  2 +-
 esm/serialize.js   |  4 ++--
 test/index.js      | 23 +++++++++++++++++++++++
 5 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/cjs/deserialize.js b/cjs/deserialize.js
index 6ce37b0..bef963b 100644
--- a/cjs/deserialize.js
+++ b/cjs/deserialize.js
@@ -65,7 +65,7 @@ const deserializer = ($, _) => {
       }
       case ERROR: {
         const {name, message} = value;
-        return as(guard(name, message), index);
+        return as(typeof env[name] === 'function' ? guard(name, message) : new Error(message), index);
       }
       case BIGINT:
         return as(BigInt(value), index);
diff --git a/cjs/serialize.js b/cjs/serialize.js
index ac6cec1..0998efe 100644
--- a/cjs/serialize.js
+++ b/cjs/serialize.js
@@ -34,8 +34,8 @@ const typeOf = value => {
   if (asString.includes('Array'))
     return [ARRAY, asString];
 
-  if (asString.includes('Error'))
-    return [ERROR, asString];
+  if (value instanceof Error)
+    return [ERROR, value.name];
 
   return [OBJECT, asString];
 };
diff --git a/esm/deserialize.js b/esm/deserialize.js
index 440fb30..e6d00c9 100644
--- a/esm/deserialize.js
+++ b/esm/deserialize.js
@@ -67,7 +67,7 @@ const deserializer = ($, _) => {
       }
       case ERROR: {
         const {name, message} = value;
-        return as(guard(name, message), index);
+        return as(typeof env[name] === 'function' ? guard(name, message) : new Error(message), index);
       }
       case BIGINT:
         return as(BigInt(value), index);
diff --git a/esm/serialize.js b/esm/serialize.js
index 24cfe2c..98fb6dd 100644
--- a/esm/serialize.js
+++ b/esm/serialize.js
@@ -36,8 +36,8 @@ const typeOf = value => {
   if (asString.includes('Array'))
     return [ARRAY, asString];
 
-  if (asString.includes('Error'))
-    return [ERROR, asString];
+  if (value instanceof Error)
+    return [ERROR, value.name];
 
   return [OBJECT, asString];
 };
diff --git a/test/index.js b/test/index.js
index 0277401..87b54b4 100644
--- a/test/index.js
+++ b/test/index.js
@@ -168,4 +168,27 @@ const invalidViaJSON = parse(stringify(invalidDate));
 assert(invalidViaJSON instanceof Date, true);
 assert(Number.isNaN(invalidViaJSON.getTime()), true);
 
+// error subtypes must round-trip to their own constructor like native structuredClone
+for (const Class of [Error, EvalError, RangeError, ReferenceError, SyntaxError, TypeError, URIError]) {
+  const errorViaRecord = deserialize(serialize(new Class('boom')));
+  assert(errorViaRecord instanceof Class, true, `${Class.name} must clone as ${Class.name}`);
+  assert(errorViaRecord.name, Class.name);
+  assert(errorViaRecord.message, 'boom');
+}
+
+// a custom-named error (name is not a global constructor) must serialize its real name,
+// then revive as a plain Error, exactly like native structuredClone does
+{
+  const custom = new Error('boom');
+  custom.name = 'CustomBunError';
+  // serialize must preserve the actual name, not fall back to 'Error'
+  assert(serialize(custom)[0][1].name, 'CustomBunError', 'serialize must preserve the custom error name');
+  const viaRecord = deserialize(serialize(custom));
+  const native = globalThis.structuredClone(custom);
+  assert(viaRecord instanceof Error, true, 'custom error must revive as Error');
+  assert(viaRecord.constructor, native.constructor, 'custom error must match native constructor');
+  assert(viaRecord.message, native.message);
+  assert(viaRecord.name, native.name);
+}
+
 require('./eval.js');