fix: issue #98

Inspect the stack to discover when a property is defined. Also fixes
an issue where a supplied (but undefined) value on the rhs would not be
detected when the lhs property is not supplied.

index.js

@@ -150,22 +150,22 @@ function deepDiff(lhs, rhs, changes, prefilter, path, key, stack) {
 
   var ltype = typeof lhs;
   var rtype = typeof rhs;
-  if (ltype === 'undefined') {
-    if (rtype !== 'undefined') {
-      changes(new DiffNew(currentPath, rhs));
-    } else {
-      changes(new DiffDeleted(currentPath, lhs));
-    }
-  } else if (rtype === 'undefined') {
+
+  var ldefined = ltype !== 'undefined' || stack && stack[stack.length - 1].lhs.hasOwnProperty(key)
+  var rdefined = rtype !== 'undefined' || stack && stack[stack.length - 1].rhs.hasOwnProperty(key)
+
+  if (!ldefined && rdefined) {
+    changes(new DiffNew(currentPath, rhs));
+  } else if (!rdefined && ldefined) {
     changes(new DiffDeleted(currentPath, lhs));
   } else if (realTypeOf(lhs) !== realTypeOf(rhs)) {
     changes(new DiffEdit(currentPath, lhs, rhs));
   } else if (realTypeOf(lhs) === 'date' && (lhs - rhs) !== 0) {
     changes(new DiffEdit(currentPath, lhs, rhs));
   } else if (ltype === 'object' && lhs !== null && rhs !== null) {
     stack = stack || [];
-    if (stack.indexOf(lhs) < 0) {
-      stack.push(lhs);
+    if (!stack.filter(function (x) { return x.lhs === lhs }).length) {
+      stack.push({ lhs: lhs, rhs: rhs });
       if (Array.isArray(lhs)) {
         var i, len = lhs.length;
         for (i = 0; i < lhs.length; i++) {

test/tests.js

@@ -565,11 +565,9 @@ describe('deep-diff', function() {
     });
 
     describe('regression test for issue #70', function() {
-        var lhs = {foo: undefined };
-        var rhs = {};
 
-        it('should detect a difference', function() {
-            var diff = deep.diff(lhs, rhs);
+        it('should detect a difference with undefined property on lhs', function() {
+            var diff = deep.diff({foo: undefined }, {});
 
             expect(diff.length).to.be(1);
 
@@ -580,6 +578,31 @@ describe('deep-diff', function() {
             expect(diff[0].lhs).to.be(undefined);
 
         });
+
+        it('should detect a difference with undefined property on rhs', function() {
+            var diff = deep.diff({}, { foo: undefined });
+
+            expect(diff.length).to.be(1);
+
+            expect(diff[0].kind).to.be('N');
+            expect(diff[0].path).to.be.an('array');
+            expect(diff[0].path).to.have.length(1);
+            expect(diff[0].path[0]).to.be('foo');
+            expect(diff[0].rhs).to.be(undefined);
+
+        });
+    });
+
+    describe('regression test for issue #98', function() {
+        var lhs = {foo: undefined };
+        var rhs = {foo: undefined };
+
+        it('should not detect a difference with two undefined property values', function() {
+            var diff = deep.diff(lhs, rhs);
+
+            expect(diff).to.be(undefined);
+
+        });
     });