[BUGFIX] do not throw on deepFreezeValue with objects with properties that are JS Proxy instances

packages/shared/util/Recoil_deepFreezeValue.js

@@ -83,7 +83,17 @@ function deepFreezeValue(value: mixed) {
     if (Object.prototype.hasOwnProperty.call(value, key)) {
       const prop = value[key];
       // Prevent infinite recurssion for circular references.
-      if (typeof prop === 'object' && prop != null && !Object.isFrozen(prop)) {
+      const objectNotFrozen = typeof prop === 'object' && prop != null && !Object.isFrozen(prop);
+
+      // Don't try to freeze proxy objects
+      // 1. Object.freeze() on a proxy proxy with not frozen target will throw
+      // 2. Freeze of the proxy target can break proxy handler behavior
+      // 3. So with 1 and 2, better to leave proxy frozen state up to consumer
+      const isObjectAProxy = prop !== null 
+        && typeof prop === 'object' 
+        && Object.getPrototypeOf(prop) !== Object.getPrototypeOf({});
+
+      if (objectNotFrozen && !isObjectAProxy) {
         deepFreezeValue(prop);
       }
     }

packages/shared/util/__tests__/Recoil_deepFreezeValue-test.js

@@ -43,6 +43,14 @@ describe('deepFreezeValue', () => {
     ).not.toThrow();
   });
 
+  test('don\'t freeze Proxy objects', () => {
+    const obj = {test: new Proxy({}, {})};
+    expect(() => deepFreezeValue(obj)).not.toThrow();
+    expect(() => deepFreezeValue(obj.test)).not.toThrow();
+    expect(Object.isFrozen(obj)).toBe(true);
+    expect(Object.isFrozen(obj.test)).toBe(false);
+  });
+
   test('check no error: object with Window property', () => {
     if (typeof window === 'undefined') {
       return;