Move internal modules to “internal” folder.

.internal/Hash.js

@@ -0,0 +1,34 @@
+import hashClear from './.internal/hashClear.js';
+import hashDelete from './.internal/hashDelete.js';
+import hashGet from './.internal/hashGet.js';
+import hashHas from './.internal/hashHas.js';
+import hashSet from './.internal/hashSet.js';
+
+/**
+ * Creates a hash object.
+ *
+ * @private
+ * @constructor
+ * @param {Array} [entries] The key-value pairs to cache.
+ */
+class Hash {
+  constructor(entries) {
+    let index = -1;
+    const length = entries == null ? 0 : entries.length;
+
+    this.clear();
+    while (++index < length) {
+      const entry = entries[index];
+      this.set(entry[0], entry[1]);
+    }
+  }
+}
+
+// Add methods to `Hash`.
+Hash.prototype.clear = hashClear;
+Hash.prototype['delete'] = hashDelete;
+Hash.prototype.get = hashGet;
+Hash.prototype.has = hashHas;
+Hash.prototype.set = hashSet;
+
+export default Hash;