Modularize master branch.

_MapCache.js

@@ -0,0 +1,32 @@
+import mapCacheClear from './_mapCacheClear.js';
+import mapCacheDelete from './_mapCacheDelete.js';
+import mapCacheGet from './_mapCacheGet.js';
+import mapCacheHas from './_mapCacheHas.js';
+import mapCacheSet from './_mapCacheSet.js';
+
+/**
+ * Creates a map cache object to store key-value pairs.
+ *
+ * @private
+ * @constructor
+ * @param {Array} [entries] The key-value pairs to cache.
+ */
+function MapCache(entries) {
+  var index = -1,
+      length = entries == null ? 0 : entries.length;
+
+  this.clear();
+  while (++index < length) {
+    var entry = entries[index];
+    this.set(entry[0], entry[1]);
+  }
+}
+
+// Add methods to `MapCache`.
+MapCache.prototype.clear = mapCacheClear;
+MapCache.prototype['delete'] = mapCacheDelete;
+MapCache.prototype.get = mapCacheGet;
+MapCache.prototype.has = mapCacheHas;
+MapCache.prototype.set = mapCacheSet;
+
+export default MapCache;