Handle keys that are in the default object's prototype chain.

This may seem a bit improbable at first, but I ran into this when
testing something unrelated in Firefox, which turns out to have:

  "watch" in {} === true

d3.v2.js

@@ -1709,7 +1709,7 @@ d3_selectionPrototype.data = function(data, join) {
 
       for (i = -1; ++i < n;) {
         key = join.call(node = group[i], node.__data__, i);
-        if (key in nodeByKey) {
+        if (nodeByKey.hasOwnProperty(key)) {
           exitNodes[j++] = node; // duplicate key
         } else {
           nodeByKey[key] = node;
@@ -1718,8 +1718,9 @@ d3_selectionPrototype.data = function(data, join) {
       }
 
       for (i = -1; ++i < m;) {
-        node = nodeByKey[key = join.call(groupData, nodeData = groupData[i], i)];
+        key = join.call(groupData, nodeData = groupData[i], i)
-        if (node) {
+        if (nodeByKey.hasOwnProperty(key)) {
+          node = nodeByKey[key];
           node.__data__ = nodeData;
           updateNodes[i] = node;
           enterNodes[i] = exitNodes[i] = null;
@@ -1731,7 +1732,7 @@ d3_selectionPrototype.data = function(data, join) {
       }
 
       for (i = -1; ++i < n;) {
-        if (keys[i] in nodeByKey) {
+        if (nodeByKey.hasOwnProperty(keys[i])) {
           exitNodes[i] = group[i];
         }
       }

src/core/selection-data.js

@@ -24,7 +24,7 @@ d3_selectionPrototype.data = function(data, join) {
 
       for (i = -1; ++i < n;) {
         key = join.call(node = group[i], node.__data__, i);
-        if (key in nodeByKey) {
+        if (nodeByKey.hasOwnProperty(key)) {
           exitNodes[j++] = node; // duplicate key
         } else {
           nodeByKey[key] = node;
@@ -33,8 +33,9 @@ d3_selectionPrototype.data = function(data, join) {
       }
 
       for (i = -1; ++i < m;) {
-        node = nodeByKey[key = join.call(groupData, nodeData = groupData[i], i)];
+        key = join.call(groupData, nodeData = groupData[i], i)
-        if (node) {
+        if (nodeByKey.hasOwnProperty(key)) {
+          node = nodeByKey[key];
           node.__data__ = nodeData;
           updateNodes[i] = node;
           enterNodes[i] = exitNodes[i] = null;
@@ -46,7 +47,7 @@ d3_selectionPrototype.data = function(data, join) {
       }
 
       for (i = -1; ++i < n;) {
-        if (keys[i] in nodeByKey) {
+        if (nodeByKey.hasOwnProperty(keys[i])) {
           exitNodes[i] = group[i];
         }
       }

test/core/selection-data-test.js

@@ -160,6 +160,15 @@ suite.addBatch({
       assert.domNull(exit[0][1]);
       assert.domEqual(exit[1][0], span[1][0]);
       assert.domNull(exit[1][1]);
+    },
+    "handles keys that are in the default object's prototype chain": function(span) {
+      // This also applies to the non-standard "watch" and "unwatch" in Mozilla Firefox.
+      var update = span.data(["hasOwnProperty", "isPrototypeOf", "toLocaleString", "toString", "valueOf"], String);
+      assert.domNull(update[0][0]);
+      assert.domNull(update[0][1]);
+      assert.domNull(update[0][2]);
+      assert.domNull(update[0][3]);
+      assert.domNull(update[0][4]);
     }
   }
 });