optimize res.format()

lib/response.js

@@ -344,19 +344,22 @@ res.format = function(obj){
     , req = this.req
     , next = req.next
     , accepted = req.accepted
+    , acceptedlen = accepted.length
     , type
     , key;
 
   // normalize extnames -> mime
-  for (var i = 0; i < keys.length; ++i) {
-    types.push(~keys[i].indexOf('/')
-      ? keys[i]
-      : mime.lookup(keys[i]));
+  if (acceptedlen) {
+    for (var i = 0; i < keys.length; ++i) {
+      types.push(~keys[i].indexOf('/')
+        ? keys[i]
+        : mime.lookup(keys[i]));
+    }
   }
 
   // determine most acceptable format
   out:
-  for (var i = 0, len = accepted.length; i < len; ++i) {
+  for (var i = 0; i < acceptedlen; ++i) {
     for (var j = 0, jlen = types.length; j < jlen; ++j) {
       if (accept(types[j].split('/'), accepted[i])) {
         key = keys[j];
@@ -367,7 +370,7 @@ res.format = function(obj){
   }
 
   // default to the first
-  if (!accepted.length) {
+  if (!acceptedlen) {
     key = keys[0];
     type = types[0];
   }