Adopt a Map.

src/selection/data.js

@@ -3,8 +3,6 @@ import {EnterNode} from "./enter.js";
 import array from "../array.js";
 import constant from "../constant.js";
 
-var keyPrefix = "$"; // Protect against keys like “__proto__”.
-
 function bindIndex(parent, group, enter, update, exit, data) {
   var i = 0,
       node,
@@ -34,7 +32,7 @@ function bindIndex(parent, group, enter, update, exit, data) {
 function bindKey(parent, group, enter, update, exit, data, key) {
   var i,
       node,
-      nodeByKeyValue = {},
+      nodeByKeyValue = new Map,
       groupLength = group.length,
       dataLength = data.length,
       keyValues = new Array(groupLength),
@@ -44,11 +42,11 @@ function bindKey(parent, group, enter, update, exit, data, key) {
   // If multiple nodes have the same key, the duplicates are added to exit.
   for (i = 0; i < groupLength; ++i) {
     if (node = group[i]) {
-      keyValues[i] = keyValue = keyPrefix + key.call(node, node.__data__, i, group);
-      if (keyValue in nodeByKeyValue) {
+      keyValues[i] = keyValue = key.call(node, node.__data__, i, group) + "";
+      if (nodeByKeyValue.has(keyValue)) {
         exit[i] = node;
       } else {
-        nodeByKeyValue[keyValue] = node;
+        nodeByKeyValue.set(keyValue, node);
       }
     }
   }
@@ -57,19 +55,19 @@ function bindKey(parent, group, enter, update, exit, data, key) {
   // If there a node associated with this key, join and add it to update.
   // If there is not (or the key is a duplicate), add it to enter.
   for (i = 0; i < dataLength; ++i) {
-    keyValue = keyPrefix + key.call(parent, data[i], i, data);
-    if (node = nodeByKeyValue[keyValue]) {
+    keyValue = key.call(parent, data[i], i, data) + "";
+    if (node = nodeByKeyValue.get(keyValue)) {
       update[i] = node;
       node.__data__ = data[i];
-      nodeByKeyValue[keyValue] = null;
+      nodeByKeyValue.delete(keyValue);
     } else {
       enter[i] = new EnterNode(parent, data[i]);
     }
   }
 
   // Add any remaining nodes that were not bound to data to exit.
   for (i = 0; i < groupLength; ++i) {
-    if ((node = group[i]) && (nodeByKeyValue[keyValues[i]] === node)) {
+    if ((node = group[i]) && (nodeByKeyValue.get(keyValues[i]) === node)) {
       exit[i] = node;
     }
   }