Rewrite map.

lib/index.js

@@ -182,19 +182,10 @@ const Channel = function(length = 0) {
 
       join: async (separator) => (await readOnly.values()).join(separator),
 
-      map: (callbackfn, thisArg) => {
-        const output = Channel();
-
-        (async () => {
-          await readOnly.forEach((value) =>
-            output.push(callbackfn.call(thisArg, value))
-          );
-
-          await output.close();
-        })();
-
-        return output;
-      },
+      map: (callbackfn, thisArg) =>
+        readOnly.flatMap((value) =>
+          Channel.of(callbackfn.call(thisArg, value))
+        ),
 
       readOnly: () => readOnly,