Use no-op for production instanceOf

src/__tests__/env-test.ts

@@ -0,0 +1,34 @@
+import { expect } from 'chai';
+import { describe, it } from 'mocha';
+
+const { getEnv: defaultGetEnv } = await import(`../env.js?ts${Date.now()}`);
+const { getEnv: developmentGetEnv, setEnv: developmentSetEnv } = await import(
+  `../env.js?ts${Date.now()}`
+);
+const { getEnv: productionGetEnv, setEnv: productionSetEnv } = await import(
+  `../env.js?ts${Date.now()}`
+);
+const { setEnv: repetitiveSetEnv } = await import(`../env.js?ts${Date.now()}`);
+
+describe('Env', () => {
+  it('should return undefined if environment is not set', () => {
+    expect(defaultGetEnv()).to.equal(undefined);
+  });
+
+  it('should set the environment to development', () => {
+    developmentSetEnv('development');
+    expect(developmentGetEnv()).to.equal('development');
+  });
+
+  it('should set the environment to production', () => {
+    productionSetEnv('production');
+    expect(productionGetEnv()).to.equal('production');
+  });
+
+  it('should throw if environment already set', () => {
+    repetitiveSetEnv('development');
+    expect(() => repetitiveSetEnv('production')).to.throw(
+      'Environment already set to "development", cannot be changed to "production".',
+    );
+  });
+});

src/env.ts

@@ -0,0 +1,21 @@
+import { useDevelopmentInstanceOfCheck } from './jsutils/instanceOf.js';
+
+export type Env = 'production' | 'development';
+
+let env: Env | undefined;
+
+export function setEnv(newEnv: Env): void {
+  if (env !== undefined && env !== newEnv) {
+    throw new Error(
+      `Environment already set to "${env}", cannot be changed to "${newEnv}".`,
+    );
+  }
+  env = newEnv;
+  if (env === 'development') {
+    useDevelopmentInstanceOfCheck();
+  }
+}
+
+export function getEnv(): Env | undefined {
+  return env;
+}

src/index.ts

@@ -28,6 +28,8 @@
 
 // The GraphQL.js version info.
 export { version, versionInfo } from './version.js';
+export { setEnv, getEnv } from './env.js';
+export type { Env } from './env.js';
 
 // The primary entry point into fulfilling a GraphQL request.
 export type { GraphQLArgs } from './graphql.js';

src/jsutils/__tests__/instanceOf-test.ts

@@ -1,9 +1,20 @@
 import { expect } from 'chai';
-import { describe, it } from 'mocha';
+import { before, describe, it } from 'mocha';
+
+import { setEnv } from '../../env.js';
 
 import { instanceOf } from '../instanceOf.js';
 
+// will pick up non-development version of instanceOf by default
+const { instanceOf: defaultInstanceOf } = await import(
+  `../instanceOf.js?ts${Date.now()}`
+);
+
 describe('instanceOf', () => {
+  before(() => {
+    setEnv('development');
+  });
+
   it('do not throw on values without prototype', () => {
     class Foo {
       get [Symbol.toStringTag]() {
@@ -16,7 +27,7 @@ describe('instanceOf', () => {
     expect(instanceOf(Object.create(null), Foo)).to.equal(false);
   });
 
-  it('detect name clashes with older versions of this lib', () => {
+  it('detect name clashes with older versions of this lib when set', () => {
     function oldVersion() {
       class Foo {}
       return Foo;
@@ -37,6 +48,27 @@ describe('instanceOf', () => {
     expect(() => instanceOf(new OldClass(), NewClass)).to.throw();
   });
 
+  it('ignore name clashes with older versions of this lib by default', () => {
+    function oldVersion() {
+      class Foo {}
+      return Foo;
+    }
+
+    function newVersion() {
+      class Foo {
+        get [Symbol.toStringTag]() {
+          return 'Foo';
+        }
+      }
+      return Foo;
+    }
+
+    const NewClass = newVersion();
+    const OldClass = oldVersion();
+    expect(defaultInstanceOf(new NewClass(), NewClass)).to.equal(true);
+    expect(defaultInstanceOf(new OldClass(), NewClass)).to.equal(false);
+  });
+
   it('allows instances to have share the same constructor name', () => {
     function getMinifiedClass(tag: string) {
       class SomeNameAfterMinification {

src/jsutils/instanceOf.ts

@@ -1,40 +1,45 @@
 import { inspect } from './inspect.js';
 
-/* c8 ignore next 3 */
-const isProduction =
-  globalThis.process != null &&
-  // eslint-disable-next-line no-undef
-  process.env.NODE_ENV === 'production';
+const noOp = (_value: unknown, _constructor: Constructor): void => {
+  /* no-op */
+};
+
+let check = noOp;
+
+export function useDevelopmentInstanceOfCheck(): void {
+  check = developmentInstanceOfCheck;
+}
 
 /**
  * A replacement for instanceof which includes an error warning when multi-realm
  * constructors are detected.
  * See: https://expressjs.com/en/advanced/best-practice-performance.html#set-node_env-to-production
  * See: https://webpack.js.org/guides/production/
  */
-export const instanceOf: (value: unknown, constructor: Constructor) => boolean =
-  /* c8 ignore next 6 */
-  // FIXME: https://github.com/graphql/graphql-js/issues/2317
-  isProduction
-    ? function instanceOf(value: unknown, constructor: Constructor): boolean {
-        return value instanceof constructor;
-      }
-    : function instanceOf(value: unknown, constructor: Constructor): boolean {
-        if (value instanceof constructor) {
-          return true;
-        }
-        if (typeof value === 'object' && value !== null) {
-          // Prefer Symbol.toStringTag since it is immune to minification.
-          const className = constructor.prototype[Symbol.toStringTag];
-          const valueClassName =
-            // We still need to support constructor's name to detect conflicts with older versions of this library.
-            Symbol.toStringTag in value
-              ? value[Symbol.toStringTag]
-              : value.constructor?.name;
-          if (className === valueClassName) {
-            const stringifiedValue = inspect(value);
-            throw new Error(
-              `Cannot use ${className} "${stringifiedValue}" from another module or realm.
+export function instanceOf(value: unknown, constructor: Constructor): boolean {
+  if (value instanceof constructor) {
+    return true;
+  }
+  check(value, constructor);
+  return false;
+}
+
+function developmentInstanceOfCheck(
+  value: unknown,
+  constructor: Constructor,
+): void {
+  if (typeof value === 'object' && value !== null) {
+    // Prefer Symbol.toStringTag since it is immune to minification.
+    const className = constructor.prototype[Symbol.toStringTag];
+    const valueClassName =
+      // We still need to support constructor's name to detect conflicts with older versions of this library.
+      Symbol.toStringTag in value
+        ? value[Symbol.toStringTag]
+        : value.constructor?.name;
+    if (className === valueClassName) {
+      const stringifiedValue = inspect(value);
+      throw new Error(
+        `Cannot use ${className} "${stringifiedValue}" from another module or realm.
 
 Ensure that there is only one instance of "graphql" in the node_modules
 directory. If different versions of "graphql" are the dependencies of other
@@ -46,11 +51,10 @@ Duplicate "graphql" modules cannot be used at the same time since different
 versions may have different capabilities and behavior. The data from one
 version used in the function from another could produce confusing and
 spurious results.`,
-            );
-          }
-        }
-        return false;
-      };
+      );
+    }
+  }
+}
 
 interface Constructor {
   prototype: {