diff --git a/lib/jfogs.js b/lib/jfogs.js
index 2fede0e..2b0ff1a 100644
--- a/lib/jfogs.js
+++ b/lib/jfogs.js
@@ -5,7 +5,7 @@
  * Javascript code obfuscator
  * @author
  *   zswang (http://weibo.com/zswang)
- * @version 0.0.6
+ * @version 0.0.7
  * @date 2015-08-23
  */
 var esprima = require('esprima');
@@ -40,14 +40,14 @@ function format(template, json) {
  * @return {String} 返回混淆后的代码
  */
 function obfuscate(code, options) {
-  function identFrom(index) {
-    prefix = options.prefix || '$fog$';
-    return prefix + index;
-  }
   if (!code) {
     return code;
   }
   options = options || {};
+  var prefix = options.prefix || '$fog$';
+  function identFrom(index) {
+    return prefix + index;
+  }
   code = String(code).replace(/\r\n?|[\n\u2028\u2029]/g, '\n')
     .replace(/^\uFEFF/, ''); // 数据清洗
   var syntax = esprima.parse(code, {
diff --git a/package.json b/package.json
index 40c21f8..6d4cfe7 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "jfogs",
-  "version": "0.0.6",
+  "version": "0.0.7",
   "description": "Javascript code obfuscator",
   "main": "index.js",
   "bin": {
diff --git a/src/jfogs.js b/src/jfogs.js
index 573ac00..6a8ada7 100644
--- a/src/jfogs.js
+++ b/src/jfogs.js
@@ -65,15 +65,15 @@ function format(template, json) {
  * @return {String} 返回混淆后的代码
  */
 function obfuscate(code, options) {
-  function identFrom(index) {
-    prefix = options.prefix || '$fog$';
-    return prefix + index;
-  }
-
   if (!code) {
     return code;
   }
   options = options || {};
+  var prefix = options.prefix || '$fog$';
+
+  function identFrom(index) {
+    return prefix + index;
+  }
 
   code = String(code).replace(/\r\n?|[\n\u2028\u2029]/g, '\n')
     .replace(/^\uFEFF/, ''); // 数据清洗