Fix interpolation of inherited object properties.

d3.v2.js

@@ -1006,16 +1006,20 @@ d3.interpolateArray = function(a, b) {
 d3.interpolateObject = function(a, b) {
   var i = {},
       c = {},
+      a_ = {},
+      b_ = {},
       k;
+  // Workaround for inconsistent behavior of propertyIsEnumerable.
+  for (k in b) b_[k] = b[k];
   for (k in a) {
-    if (b.propertyIsEnumerable(k)) {
-      i[k] = d3_interpolateByName(k)(a[k], b[k]);
+    if (Object.hasOwnProperty.call(b_, k)) {
+      i[k] = d3_interpolateByName(k)(a_[k] = a[k], b[k]);
     } else {
-      c[k] = a[k];
+      c[k] = a_[k] = a[k];
     }
   }
   for (k in b) {
-    if (!a.propertyIsEnumerable(k)) {
+    if (!Object.hasOwnProperty.call(a_, k)) {
       c[k] = b[k];
     }
   }

src/core/interpolate.js

@@ -194,16 +194,20 @@ d3.interpolateArray = function(a, b) {
 d3.interpolateObject = function(a, b) {
   var i = {},
       c = {},
+      a_ = {},
+      b_ = {},
       k;
+  // Workaround for inconsistent behavior of propertyIsEnumerable.
+  for (k in b) b_[k] = b[k];
   for (k in a) {
-    if (b.propertyIsEnumerable(k)) {
-      i[k] = d3_interpolateByName(k)(a[k], b[k]);
+    if (Object.hasOwnProperty.call(b_, k)) {
+      i[k] = d3_interpolateByName(k)(a_[k] = a[k], b[k]);
     } else {
-      c[k] = a[k];
+      c[k] = a_[k] = a[k];
     }
   }
   for (k in b) {
-    if (!a.propertyIsEnumerable(k)) {
+    if (!Object.hasOwnProperty.call(a_, k)) {
       c[k] = b[k];
     }
   }

test/core/interpolate-test.js

@@ -30,6 +30,11 @@ suite.addBatch({
     "interpolates objects with default object prototype properties": function(interpolate) {
       assert.deepEqual(interpolate({foo: 2, hasOwnProperty: 1}, {foo: 12})(1), {foo: 12, hasOwnProperty: 1});
     },
+    "interpolates inherited properties of objects": function(interpolate) {
+      var a = Object.create({foo: 0}),
+          b = Object.create({foo: 2});
+      assert.deepEqual(interpolate(a, b)(.5), {foo: 1});
+    },
     "doesn't interpret properties in the default object's prototype chain as RGB": function(interpolate) {
       assert.equal(interpolate("hasOwnProperty", "hasOwnProperty")(0), "hasOwnProperty");
     }