+ /**
+ * Make a versioned key for a specific module.
+ *
+ * @private
+ * @param {string} module Module name
+ * @return {string|null} Module key in format '`[name]@[version]`',
+ * or null if the module does not exist
+ */
+ function getModuleKey( module ) {
+ return hasOwn.call( registry, module ) ?
+ ( module + '@' + registry[ module ].version ) : null;
+ }
+
+ /**
+ * @private
+ * @param {string} key Module name or '`[name]@[version]`'
+ * @return {Object}
+ */
+ function splitModuleKey( key ) {
+ var index = key.indexOf( '@' );
+ if ( index === -1 ) {
+ return { name: key };
+ }
+ return {
+ name: key.slice( 0, index ),
+ version: key.slice( index )
+ };
+ }
+