handle external proxification (#53)

skip generation of a replace operation, if an object within the tree is replaced with a proxified version of itself by external code

src/jsonpatcherproxy.js

@@ -85,6 +85,10 @@ const JSONPatcherProxy = (function() {
     if (isObject(newValue)) {
       const subtreeMetadata = newValue[instance._metadataSymbol];
       if (subtreeMetadata) {
+        if(subtreeMetadata.parent === tree && subtreeMetadata.keyInParent === key) {
+          //this is the same object that we already proxified, proxified now by someone else. In this case, remain silent
+          return Reflect.set(tree, key, newValue);
+        }
         subtreeMetadata.parent = tree;
         subtreeMetadata.keyInParent = key;
         /*

test/spec/proxySpec.js

@@ -271,6 +271,30 @@ describe('proxy', function() {
       obj2.phoneNumbers[1].number = '456';
       expect(observedObj).toReallyEqual(obj2); //objects should be still the same
     });
+
+    it('should generate replace (deep object, proxified)', function() {
+      const obj = generateDeepObjectFixture();
+      const jsonPatcherProxy = new JSONPatcherProxy(obj);
+      let observedObj = jsonPatcherProxy.observe(true);
+
+      //begin external proxification
+      observedObj = new Proxy(observedObj, {});
+      observedObj.phoneNumbers = new Proxy(observedObj.phoneNumbers, {});
+      observedObj.phoneNumbers[0] = new Proxy(observedObj.phoneNumbers[0], {});
+      observedObj.phoneNumbers[1] = new Proxy(observedObj.phoneNumbers[1], {});
+      //end external proxification
+
+      observedObj.phoneNumbers[0].number = '123';
+
+      const patches = jsonPatcherProxy.generate();
+      expect(patches).toReallyEqual([
+        {
+          op: 'replace',
+          path: '/phoneNumbers/0/number',
+          value: '123'
+        }
+      ]);
+    });
 
     it('should generate replace (changes in new array cell, primitive values)', function() {
       var arr = [1];