Bump to v4.0.0.

internal/hashHas.js

@@ -0,0 +1,21 @@
+var nativeCreate = require('./nativeCreate');
+
+/** Used for built-in method references. */
+var objectProto = global.Object.prototype;
+
+/** Used to check objects for own properties. */
+var hasOwnProperty = objectProto.hasOwnProperty;
+
+/**
+ * Checks if a hash value for `key` exists.
+ *
+ * @private
+ * @param {Object} hash The hash to query.
+ * @param {string} key The key of the entry to check.
+ * @returns {boolean} Returns `true` if an entry for `key` exists, else `false`.
+ */
+function hashHas(hash, key) {
+  return nativeCreate ? hash[key] !== undefined : hasOwnProperty.call(hash, key);
+}
+
+module.exports = hashHas;