diff --git a/.campaign/tgz/SHA256SUMS b/.campaign/tgz/SHA256SUMS
index f78f4a2..fd6c1f9 100644
--- a/.campaign/tgz/SHA256SUMS
+++ b/.campaign/tgz/SHA256SUMS
@@ -1,6 +1,6 @@
 abdbff87d78af3f605b465b1104c9a57fa859fbc14d8bb9ba396a49869269d99  antelopejs-api-6afe3e2.tgz
 0a51c9c2da58c2586bfa5095b1da92a7b74130acf1e64820bfd5f98eaa4200f9  antelopejs-core-184eb90.tgz
-8e017528574748687b246df07affa6cbcfbe931cc6086fcb5dd2c7a28c1f0d8e  antelopejs-interface-api-015a93a.tgz
+1a29379d519467fdd438ee411a93519956f1e024d4f457f0d447cac67af61099  antelopejs-interface-api-fcc62d2.tgz
 fa0a3cfa243d0c78cd29d45839ae61bbbce5615a7c8d8247755b0cd91c8bedc6  antelopejs-interface-api-util-639f38b.tgz
 30391718e65481815db5b5bb10e7eabb1feac13165005ee46e54b592f3676c69  antelopejs-interface-core-f7df541.tgz
 ccdc833729f50825d3567047a22bf9c68f47a38ca3527117756fbd80f380fabd  antelopejs-interface-database-724ff72.tgz
diff --git a/.campaign/tgz/antelopejs-interface-api-015a93a.tgz b/.campaign/tgz/antelopejs-interface-api-015a93a.tgz
deleted file mode 100644
index a14002a..0000000
Binary files a/.campaign/tgz/antelopejs-interface-api-015a93a.tgz and /dev/null differ
diff --git a/.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz b/.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz
new file mode 100644
index 0000000..19969c5
Binary files /dev/null and b/.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz differ
diff --git a/README.md b/README.md
index c4b3df0..b22e968 100644
--- a/README.md
+++ b/README.md
@@ -125,7 +125,7 @@ The package declares these `@antelopejs/*` peer dependencies:
 
 | Package                                     | Supported         | Tested with                                                               |
 | ------------------------------------------- | ----------------- | ------------------------------------------------------------------------- |
-| `@antelopejs/interface-api`                 | `>=0.3.0 <1.0.0`  | `file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz`                 |
+| `@antelopejs/interface-api`                 | `>=0.3.0 <1.0.0`  | `file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz`                 |
 | `@antelopejs/interface-api-util`            | `>=0.1.3 <1.0.0`  | `file:.campaign/tgz/antelopejs-interface-api-util-639f38b.tgz`            |
 | `@antelopejs/interface-core`                | `>=0.2.4 <1.0.0`  | `file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz`                |
 | `@antelopejs/interface-database`            | `>=0.1.10 <1.0.0` | `file:.campaign/tgz/antelopejs-interface-database-724ff72.tgz`            |
diff --git a/package.json b/package.json
index 3713ba2..e6f15db 100644
--- a/package.json
+++ b/package.json
@@ -73,7 +73,7 @@
   "devDependencies": {
     "@antelopejs/api": "file:.campaign/tgz/antelopejs-api-6afe3e2.tgz",
     "@antelopejs/core": "file:.campaign/tgz/antelopejs-core-184eb90.tgz",
-    "@antelopejs/interface-api": "file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz",
+    "@antelopejs/interface-api": "file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz",
     "@antelopejs/interface-api-util": "file:.campaign/tgz/antelopejs-interface-api-util-639f38b.tgz",
     "@antelopejs/interface-core": "file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz",
     "@antelopejs/interface-database": "file:.campaign/tgz/antelopejs-interface-database-724ff72.tgz",
@@ -109,7 +109,7 @@
     "overrides": {
       "@antelopejs/interface-database": "file:.campaign/tgz/antelopejs-interface-database-724ff72.tgz",
       "@antelopejs/interface-database-decorators": "file:.campaign/tgz/antelopejs-interface-database-decorators-1234214.tgz",
-      "@antelopejs/interface-api": "file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz",
+      "@antelopejs/interface-api": "file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz",
       "@antelopejs/interface-api-util": "file:.campaign/tgz/antelopejs-interface-api-util-639f38b.tgz",
       "@antelopejs/api": "file:.campaign/tgz/antelopejs-api-6afe3e2.tgz",
       "@antelopejs/interface-core": "file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index e2d9042..259de5b 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -7,7 +7,7 @@ settings:
 overrides:
   '@antelopejs/interface-database': file:.campaign/tgz/antelopejs-interface-database-724ff72.tgz
   '@antelopejs/interface-database-decorators': file:.campaign/tgz/antelopejs-interface-database-decorators-1234214.tgz
-  '@antelopejs/interface-api': file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz
+  '@antelopejs/interface-api': file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz
   '@antelopejs/interface-api-util': file:.campaign/tgz/antelopejs-interface-api-util-639f38b.tgz
   '@antelopejs/api': file:.campaign/tgz/antelopejs-api-6afe3e2.tgz
   '@antelopejs/interface-core': file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz
@@ -18,11 +18,11 @@ importers:
   .:
     dependencies:
       '@antelopejs/interface-api':
-        specifier: file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz
-        version: file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)
+        specifier: file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz
+        version: file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)
       '@antelopejs/interface-api-util':
         specifier: file:.campaign/tgz/antelopejs-interface-api-util-639f38b.tgz
-        version: file:.campaign/tgz/antelopejs-interface-api-util-639f38b.tgz(@antelopejs/interface-api@file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz))(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)
+        version: file:.campaign/tgz/antelopejs-interface-api-util-639f38b.tgz(@antelopejs/interface-api@file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz))(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)
       '@antelopejs/interface-core':
         specifier: file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz
         version: file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz
@@ -31,7 +31,7 @@ importers:
         version: file:.campaign/tgz/antelopejs-interface-database-724ff72.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)
       '@antelopejs/interface-database-decorators':
         specifier: file:.campaign/tgz/antelopejs-interface-database-decorators-1234214.tgz
-        version: file:.campaign/tgz/antelopejs-interface-database-decorators-1234214.tgz(@antelopejs/interface-api@file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz))(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)(@antelopejs/interface-database@file:.campaign/tgz/antelopejs-interface-database-724ff72.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz))
+        version: file:.campaign/tgz/antelopejs-interface-database-decorators-1234214.tgz(@antelopejs/interface-api@file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz))(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)(@antelopejs/interface-database@file:.campaign/tgz/antelopejs-interface-database-724ff72.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz))
     devDependencies:
       '@antelopejs/api':
         specifier: file:.campaign/tgz/antelopejs-api-6afe3e2.tgz
@@ -118,8 +118,8 @@ packages:
       '@antelopejs/interface-api': '>=0.3.0 <1.0.0'
       '@antelopejs/interface-core': '>=0.2.4 <1.0.0'
 
-  '@antelopejs/interface-api@file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz':
-    resolution: {integrity: sha512-G7BRef+991Dn+O4zmxGE8f8KN5Xfj5GQa+W3LQo0f+XHhRUCz2E+brTIonhjV7HJ5Z+lFNrm4StPytwNIUxA5Q==, tarball: file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz}
+  '@antelopejs/interface-api@file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz':
+    resolution: {integrity: sha512-6A2dS+0P6O+AGI9Jjq+6vGflWsDC3S6BinYeNiqvQxK2ggebzt1sq1jstRmlFZWfW5/lxemjBmtwCtfXzLfXVA==, tarball: file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz}
     version: 0.3.0
     peerDependencies:
       '@antelopejs/interface-core': '>=0.4.0 <1.0.0'
@@ -2836,8 +2836,8 @@ snapshots:
 
   '@antelopejs/api@file:.campaign/tgz/antelopejs-api-6afe3e2.tgz(@antelopejs/core@file:.campaign/tgz/antelopejs-core-184eb90.tgz)':
     dependencies:
-      '@antelopejs/interface-api': file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)
-      '@antelopejs/interface-api-util': file:.campaign/tgz/antelopejs-interface-api-util-639f38b.tgz(@antelopejs/interface-api@file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz))(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)
+      '@antelopejs/interface-api': file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)
+      '@antelopejs/interface-api-util': file:.campaign/tgz/antelopejs-interface-api-util-639f38b.tgz(@antelopejs/interface-api@file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz))(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)
       '@antelopejs/interface-core': file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz
       reflect-metadata: 0.2.2
       ws: 8.22.1
@@ -2862,12 +2862,12 @@ snapshots:
       semver: 7.7.4
       typescript: 5.9.3
 
-  '@antelopejs/interface-api-util@file:.campaign/tgz/antelopejs-interface-api-util-639f38b.tgz(@antelopejs/interface-api@file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz))(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)':
+  '@antelopejs/interface-api-util@file:.campaign/tgz/antelopejs-interface-api-util-639f38b.tgz(@antelopejs/interface-api@file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz))(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)':
     dependencies:
-      '@antelopejs/interface-api': file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)
+      '@antelopejs/interface-api': file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)
       '@antelopejs/interface-core': file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz
 
-  '@antelopejs/interface-api@file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)':
+  '@antelopejs/interface-api@file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)':
     dependencies:
       '@antelopejs/interface-core': file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz
 
@@ -2875,9 +2875,9 @@ snapshots:
     dependencies:
       reflect-metadata: 0.2.2
 
-  '@antelopejs/interface-database-decorators@file:.campaign/tgz/antelopejs-interface-database-decorators-1234214.tgz(@antelopejs/interface-api@file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz))(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)(@antelopejs/interface-database@file:.campaign/tgz/antelopejs-interface-database-724ff72.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz))':
+  '@antelopejs/interface-database-decorators@file:.campaign/tgz/antelopejs-interface-database-decorators-1234214.tgz(@antelopejs/interface-api@file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz))(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)(@antelopejs/interface-database@file:.campaign/tgz/antelopejs-interface-database-724ff72.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz))':
     dependencies:
-      '@antelopejs/interface-api': file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)
+      '@antelopejs/interface-api': file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)
       '@antelopejs/interface-core': file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz
       '@antelopejs/interface-database': file:.campaign/tgz/antelopejs-interface-database-724ff72.tgz(@antelopejs/interface-core@file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz)
       randomstring: 1.3.1
diff --git a/pnpm-workspace.yaml b/pnpm-workspace.yaml
index 0e3a33c..91985f3 100644
--- a/pnpm-workspace.yaml
+++ b/pnpm-workspace.yaml
@@ -1,7 +1,7 @@
 overrides:
   "@antelopejs/interface-database": "file:.campaign/tgz/antelopejs-interface-database-724ff72.tgz"
   "@antelopejs/interface-database-decorators": "file:.campaign/tgz/antelopejs-interface-database-decorators-1234214.tgz"
-  "@antelopejs/interface-api": "file:.campaign/tgz/antelopejs-interface-api-015a93a.tgz"
+  "@antelopejs/interface-api": "file:.campaign/tgz/antelopejs-interface-api-fcc62d2.tgz"
   "@antelopejs/interface-api-util": "file:.campaign/tgz/antelopejs-interface-api-util-639f38b.tgz"
   "@antelopejs/api": "file:.campaign/tgz/antelopejs-api-6afe3e2.tgz"
   "@antelopejs/interface-core": "file:.campaign/tgz/antelopejs-interface-core-f7df541.tgz"
diff --git a/src/components.ts b/src/components.ts
index 9d9c9db..96c65d8 100644
--- a/src/components.ts
+++ b/src/components.ts
@@ -37,6 +37,7 @@ import { isString } from "./internal/guards";
 import * as joined from "./internal/joined";
 import * as list from "./internal/list";
 import * as properties from "./internal/properties";
+import { fieldsOf } from "./internal/prototypes";
 import { ReadProperties as readProperties } from "./internal/read-properties";
 import * as tables from "./internal/tables";
 import * as validation from "./internal/validation";
@@ -271,7 +272,7 @@ export namespace Query {
     meta: DataAPIMeta,
   ): ModelInstance {
     assert(meta.modelKey, 500, "Missing model key.");
-    const model: unknown = obj[meta.modelKey];
+    const model = fieldsOf(obj)[meta.modelKey];
     assert(
       tables.isModelInstance(model),
       500,
diff --git a/src/index.ts b/src/index.ts
index 9b1c149..f38741d 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -84,7 +84,7 @@ export function DataController<
         ? { endpoint: key, callback: val }
         : { endpoint: key, ...val };
     meta.addEndpoint(key, entry);
-    c.prototype[key] = entry.callback.func;
+    Object.assign(c.prototype, { [key]: entry.callback.func });
   }
   // SAFETY: for every own key of def, the loop above installs the function ExtractCallback<P[key]> names (def[key].func, or def[key].callback.func for an entry with options) on c.prototype, which covers the members of ExtractDefCallbacks<P>; c extends base and declares table itself.
   return c as Class<ExtractDefCallbacks<P> & TableHolder<C>> & Base;
diff --git a/src/internal/properties.ts b/src/internal/properties.ts
index 2332ac4..c4a526e 100644
--- a/src/internal/properties.ts
+++ b/src/internal/properties.ts
@@ -7,7 +7,7 @@ import type {
   RowFields,
   WritableAccessFields,
 } from "../metadata";
-import { prototypeOf } from "./prototypes";
+import { fieldsOf, prototypeOf } from "./prototypes";
 
 function writableInBody(
   writable: WritableAccessFields,
@@ -20,7 +20,7 @@ function writableInBody(
 }
 
 function writeTargetDefaults(
-  instance: Parameters<typeof Query.WriteProperties>[0],
+  instance: RowFields,
   meta: DataAPIMeta,
   dbData: RowFields,
 ) {
@@ -47,7 +47,7 @@ export function WriteProperties(
   const writable = existingDBData
     ? writableInBody(actionWritable, bodyData)
     : actionWritable;
-  const instance = { ...obj };
+  const instance = fieldsOf({ ...obj });
   const dbData: RowFields = existingDBData || {};
   Object.setPrototypeOf(dbData, prototypeOf(meta.tableClass));
   if (!existingDBData) {
diff --git a/src/internal/prototypes.ts b/src/internal/prototypes.ts
index 702b77c..9ab5494 100644
--- a/src/internal/prototypes.ts
+++ b/src/internal/prototypes.ts
@@ -3,8 +3,25 @@
 import type { Class } from "@antelopejs/interface-core/decorators";
 
 import type { DataControllerInstance } from "./controller-types";
+import type { RowFields } from "./field-types";
 import { isClass, isObject } from "./guards";
 
+/**
+ * A controller instance read by field name: an object answers every string key,
+ * with `undefined` for a field it lacks, and inherited accessors run on the
+ * instance, because this is the instance itself.
+ */
+export function fieldsOf(instance: DataControllerInstance): RowFields {
+  if (!holdsFields(instance)) {
+    throw new TypeError("A data controller must be an object.");
+  }
+  return instance;
+}
+
+function holdsFields(instance: DataControllerInstance): instance is RowFields {
+  return isObject(instance);
+}
+
 /** The object the instances of a class inherit from. */
 export function prototypeOf(target: Class): object {
   const prototype: unknown = target.prototype;
diff --git a/src/internal/read-properties.ts b/src/internal/read-properties.ts
index 21721c7..ba3ad5e 100644
--- a/src/internal/read-properties.ts
+++ b/src/internal/read-properties.ts
@@ -6,7 +6,7 @@ import type {
   RowFields,
 } from "../metadata";
 import { isFunction } from "./guards";
-import { prototypeOf } from "./prototypes";
+import { fieldsOf, prototypeOf } from "./prototypes";
 
 export async function ReadProperties(
   obj: DataControllerInstance,
@@ -17,7 +17,7 @@ export async function ReadProperties(
 ) {
   const readable =
     meta.readable[action ?? "_default"] ?? meta.readable._default;
-  const instance = { ...obj };
+  const instance = fieldsOf({ ...obj });
   const res: RowFields = {};
   for (const [key, field] of readable.props) {
     if (onlyList && !field.listable) {
diff --git a/src/internal/validation.ts b/src/internal/validation.ts
index 8e3e1a7..29bfdb8 100644
--- a/src/internal/validation.ts
+++ b/src/internal/validation.ts
@@ -18,6 +18,7 @@ import type {
   DataControllerInstance,
   RowFields,
 } from "../metadata";
+import { fieldsOf } from "./prototypes";
 import { isFieldValues, isObject } from "./guards";
 
 type RequestBody = Validation.RequestBody;
@@ -52,7 +53,7 @@ export function Lock(
 ) {
   for (const [modifier, field] of meta.modifierKeys.entries()) {
     const keyed: KeyedModifier = modifier;
-    const key: unknown = obj[field];
+    const key = fieldsOf(obj)[field];
     lock(data, keyed, written, key);
   }
 }
@@ -72,7 +73,7 @@ export function Unlock(
   }
   for (const [modifier, field] of meta.modifierKeys.entries()) {
     const keyed: KeyedModifier = modifier;
-    const key: unknown = obj[field];
+    const key = fieldsOf(obj)[field];
     unlock(dbData, keyed, undefined, key);
     for (const [foreign, fieldData] of Object.entries(meta.fields)) {
       const related = dbData[foreign];
@@ -92,7 +93,7 @@ export function UnlockRequest<T extends {}, K extends keyof T>(
   const modifiers = Array.from(meta.modifierKeys.entries()).map(
     ([modifier, field]) => ({
       modifier,
-      args: [obj[field]],
+      args: [fieldsOf(obj)[field]],
     }),
   );
   return unlockrequest<T, K>(meta.tableClass, row, field, modifiers);
diff --git a/src/tests/internal/controller-fields.test.ts b/src/tests/internal/controller-fields.test.ts
new file mode 100644
index 0000000..d03bb44
--- /dev/null
+++ b/src/tests/internal/controller-fields.test.ts
@@ -0,0 +1,28 @@
+import assert from "node:assert";
+
+import { fieldsOf } from "../../internal/prototypes";
+
+class Holder {
+  own = "own value";
+
+  get inherited(): string {
+    return `read from ${this.own}`;
+  }
+}
+
+describe("fieldsOf", () => {
+  it("answers own fields and inherited accessors by name", () => {
+    const fields = fieldsOf(new Holder());
+
+    assert.strictEqual(fields.own, "own value");
+    assert.strictEqual(fields.inherited, "read from own value");
+    assert.strictEqual(fields.absent, undefined);
+  });
+
+  it("refuses a value that is not an object", () => {
+    assert.throws(
+      () => fieldsOf(() => undefined),
+      /A data controller must be an object/,
+    );
+  });
+});