change the behavior in case of undefined value

this is a fix for issues #105, #90, #60, #32 and a part of #76 that describes a problem with undefined
all tests pass after this commit

README.md

@@ -250,11 +250,11 @@ As `undefined` is not a valid value for any JSON node, it's also not valid value
 However, to play nicer with natural JavaScipt objects `jsonpatch` can be applied to an object that contains `undefined`, in such case we will treat it as JS does. `.apply` will handle JSON Patches with `value: undefined` as any other falsy value. `.generate`, `.compare`, `.observe` methods will also produce JSON Patches with `undefined`s, but only for (non valid) JSON documents that contains it.
 
 
-## :no_entry_sign: `undefined`s (JS to JSON projection)
+## `undefined`s (JS to JSON projection)
 
-~~As `undefined` is not a valid value for any JSON node, it's also not valid value o JSON Patch operation object value property. Therefore `jsonpatch` will not generate JSON Patches that sets anything to `undefined`.~~
+As `undefined` type does not exist in JSON, it's also not a valid value of JSON Patch operation. Therefore `jsonpatch` will not generate JSON Patches that sets anything to `undefined`.
 
-~~However, to play nicer with natural JavaScipt objects `jsonpatch` can be applied to an object that contains `undefined`, in such case we will use it as native `JSON.stringify` - we will treat them as non-existing nodes, and map to `null` for array elements.~~
+Whenever a value is set to `undefined` in JS, JSON-Patch methods `generate` and `compare` will treat it similarly to how JavaScript method `JSON.stringify` treats them. See the test suite (in the `test/` subdirectory) or the [ECMAScript spec](http://www.ecma-international.org/ecma-262/6.0/index.html#sec-json.stringify) for details.
 
 ## Changelog
 

src/json-patch-duplex.js

@@ -261,11 +261,13 @@ var jsonpatch;
     }
     jsonpatch.unobserve = unobserve;
     function deepClone(obj) {
-        if (typeof obj === "object") {
-            return JSON.parse(JSON.stringify(obj)); //Faster than ES5 clone - http://jsperf.com/deep-cloning-of-objects/5
-        }
-        else {
-            return obj; //no need to clone primitives
+        switch (typeof obj) {
+            case "object":
+                return JSON.parse(JSON.stringify(obj)); //Faster than ES5 clone - http://jsperf.com/deep-cloning-of-objects/5
+            case "undefined":
+                return null; //this is how JSON.stringify behaves for array items
+            default:
+                return obj; //no need to clone primitives
         }
     }
     function observe(obj, callback) {
@@ -359,7 +361,7 @@ var jsonpatch;
         for (var t = oldKeys.length - 1; t >= 0; t--) {
             var key = oldKeys[t];
             var oldVal = mirror[key];
-            if (obj.hasOwnProperty(key)) {
+            if (obj.hasOwnProperty(key) && !(_isArray(obj) === false && obj[key] === undefined)) {
                 var newVal = obj[key];
                 if (typeof oldVal == "object" && oldVal != null && typeof newVal == "object" && newVal != null) {
                     _generate(oldVal, newVal, patches, path + "/" + escapePathComponent(key));
@@ -381,7 +383,7 @@ var jsonpatch;
         }
         for (var t = 0; t < newKeys.length; t++) {
             var key = newKeys[t];
-            if (!mirror.hasOwnProperty(key)) {
+            if (!mirror.hasOwnProperty(key) && obj[key] !== undefined) {
                 patches.push({ op: "add", path: path + "/" + escapePathComponent(key), value: deepClone(obj[key]) });
             }
         }

src/json-patch-duplex.ts

@@ -290,11 +290,15 @@ module jsonpatch {
   }
 
   function deepClone(obj:any) {
-    if (typeof obj === "object") {
-      return JSON.parse(JSON.stringify(obj)); //Faster than ES5 clone - http://jsperf.com/deep-cloning-of-objects/5
-    }
-    else {
-      return obj; //no need to clone primitives
+    switch (typeof obj) {
+      case "object":
+        return JSON.parse(JSON.stringify(obj)); //Faster than ES5 clone - http://jsperf.com/deep-cloning-of-objects/5
+
+      case "undefined":
+        return null; //this is how JSON.stringify behaves for array items
+
+      default:
+        return obj; //no need to clone primitives
     }
   }
 
@@ -400,7 +404,7 @@ module jsonpatch {
     for (var t = oldKeys.length - 1; t >= 0; t--) {
       var key = oldKeys[t];
       var oldVal = mirror[key];
-      if (obj.hasOwnProperty(key)) {
+      if (obj.hasOwnProperty(key) && !(_isArray(obj) === false && obj[key] === undefined)) {
         var newVal = obj[key];
         if (typeof oldVal == "object" && oldVal != null && typeof newVal == "object" && newVal != null) {
           _generate(oldVal, newVal, patches, path + "/" + escapePathComponent(key));
@@ -424,7 +428,7 @@ module jsonpatch {
 
     for (var t = 0; t < newKeys.length; t++) {
       var key = newKeys[t];
-      if (!mirror.hasOwnProperty(key)) {
+      if (!mirror.hasOwnProperty(key) && obj[key] !== undefined) {
         patches.push({op: "add", path: path + "/" + escapePathComponent(key), value: deepClone(obj[key])});
       }
     }