Bump to v4.0.0.

internal/Stack.js

@@ -0,0 +1,31 @@
+import stackClear from './stackClear';
+import stackDelete from './stackDelete';
+import stackGet from './stackGet';
+import stackHas from './stackHas';
+import stackSet from './stackSet';
+
+/**
+ * Creates a stack cache object to store key-value pairs.
+ *
+ * @private
+ * @param {Array} [values] The values to cache.
+ */
+function Stack(values) {
+  var index = -1,
+      length = values ? values.length : 0;
+
+  this.clear();
+  while (++index < length) {
+    var entry = values[index];
+    this.set(entry[0], entry[1]);
+  }
+}
+
+// Add functions to the `Stack` cache.
+Stack.prototype.clear = stackClear;
+Stack.prototype['delete'] = stackDelete;
+Stack.prototype.get = stackGet;
+Stack.prototype.has = stackHas;
+Stack.prototype.set = stackSet;
+
+export default Stack;