Use a Map to accelerate seen object lookups.

index.js

@@ -1,28 +1,53 @@
-exports.encode = exports.stringify = function (value) {
- var values = [value];
+function encode(value) {
+ return JSON.stringify(tabulate(value));
+}
+
+function tabulate(value) {
+ var values = [];
  var table = [];
+ var indexMap = typeof Map === "function" && new Map;
+
+ function getIndex(value) {
+ var index;
+
+ if (indexMap) {
+ // If we have Map, use it instead of values.indexOf to accelerate
+ // object lookups.
+ index = indexMap.get(value);
+ if (typeof index === "undefined") {
+ index = values.push(value) - 1;
+ indexMap.set(value, index);
+ }
+ } else {
+ index = values.indexOf(value);
+ if (index < 0) {
+ index = values.push(value) - 1;
+ }
+ }
+
+ return index;
+ }
+
+ // Assign the root value to values[0].
+ getIndex(value);
 
  for (var v = 0; v < values.length; ++v) {
  value = values[v];
+
  if (value && typeof value === "object") {
  var copy = table[v] = Array.isArray(value) ? [] : {};
  Object.keys(value).forEach(function (key) {
- var child = value[key];
- var index = values.indexOf(child);
- if (index < 0) {
- index = values.push(child) - 1;
- }
- copy[key] = index;
+ copy[key] = getIndex(value[key]);
  });
  } else {
  table[v] = value;
  }
  }
 
- return JSON.stringify(table);
-};
+ return table;
+}
 
-exports.decode = exports.parse = function (encoding) {
+function decode(encoding) {
  var table = JSON.parse(encoding);
 
  table.forEach(function (entry) {
@@ -34,4 +59,7 @@ exports.decode = exports.parse = function (encoding) {
  });
 
  return table[0];
-};
+}
+
+exports.encode = exports.stringify = encode;
+exports.decode = exports.parse = decode;