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node_modules/graphql/jsutils/instanceOf.js.flow

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+// @flow strict
+
+/**
+ * A replacement for instanceof which includes an error warning when multi-realm
+ * constructors are detected.
+ */
+declare function instanceOf(
+  value: mixed,
+  constructor: mixed,
+): boolean %checks(value instanceof constructor);
+
+// See: https://expressjs.com/en/advanced/best-practice-performance.html#set-node_env-to-production
+// See: https://webpack.js.org/guides/production/
+export default process.env.NODE_ENV === 'production'
+  ? // eslint-disable-next-line no-shadow
+    function instanceOf(value: mixed, constructor: mixed) {
+      return value instanceof constructor;
+    }
+  : // eslint-disable-next-line no-shadow
+    function instanceOf(value: any, constructor: any) {
+      if (value instanceof constructor) {
+        return true;
+      }
+      if (value) {
+        const valueClass = value.constructor;
+        const className = constructor.name;
+        if (className && valueClass && valueClass.name === className) {
+          throw new Error(
+            `Cannot use ${className} "${value}" 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
+relied on modules, use "resolutions" to ensure only one version is installed.
+
+https://yarnpkg.com/en/docs/selective-version-resolutions
+
+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;
+    };