util: improve internal `isError()` validation

The current internal isError function checked the toString value
instead of using the more precise `util.types.isNativeError()` check.
The `instanceof` check is not removed due to possible errors that
are not native but still an instance of Error.

PR-URL: https://github.com/nodejs/node/pull/24746
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

1 files changed, 37 insertions, 0 deletions

diff --git a/test/parallel/test-internal-util-helpers.js b/test/parallel/test-internal-util-helpers.js
new file mode 100644
index 0000000000..bf60cff9bd
--- /dev/null
+++ b/test/parallel/test-internal-util-helpers.js
@@ -0,0 +1,37 @@
+// Flags: --expose-internals
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const { types } = require('util');
+const { isError } = require('internal/util');
+const vm = require('vm');
+
+// Special cased errors. Test the internal function which is used in
+// `util.inspect()`, the `repl` and maybe more. This verifies that errors from
+// different realms, and non native instances of error are properly detected as
+// error while definitely false ones are not detected. This is different than
+// the public `util.isError()` function which falsy detects the fake errors as
+// actual errors.
+{
+  const fake = { [Symbol.toStringTag]: 'Error' };
+  assert(!types.isNativeError(fake));
+  assert(!(fake instanceof Error));
+  assert(!isError(fake));
+
+  const err = new Error('test');
+  const newErr = Object.create(
+    Object.getPrototypeOf(err),
+    Object.getOwnPropertyDescriptors(err));
+  Object.defineProperty(err, 'message', { value: err.message });
+  assert(types.isNativeError(err));
+  assert(!types.isNativeError(newErr));
+  assert(newErr instanceof Error);
+  assert(isError(newErr));
+
+  const context = vm.createContext({});
+  const differentRealmErr = vm.runInContext('new Error()', context);
+  assert(types.isNativeError(differentRealmErr));
+  assert(!(differentRealmErr instanceof Error));
+  assert(isError(differentRealmErr));
+}