diff --git a/index.js b/index.js
index 644efd1..971c8b6 100644
--- a/index.js
+++ b/index.js
@@ -35,12 +35,26 @@ var defineProp = (function() {
 }());
 
 var globals = ['Array', 'Boolean', 'Date', 'Error', 'EvalError', 'Function',
-'Infinity', 'JSON', 'Math', 'NaN', 'Number', 'Object', 'RangeError',
+'JSON', 'Math', 'NaN', 'Number', 'Object', 'RangeError',
 'ReferenceError', 'RegExp', 'String', 'SyntaxError', 'TypeError', 'URIError',
 'decodeURI', 'decodeURIComponent', 'encodeURI', 'encodeURIComponent', 'escape',
 'eval', 'isFinite', 'isNaN', 'parseFloat', 'parseInt', 'undefined', 'unescape'];
 
-function Context() {}
+function Context() {
+  
+  var iframe = document.createElement('iframe');
+  if (!iframe.style) iframe.style = {};
+  iframe.style.display = 'none';
+
+  document.body.appendChild(iframe);
+
+  Object.defineProperty(this, "_iframe", {
+      enumerable: false,
+      writable: true
+  });
+
+  this._iframe = iframe;
+}
 Context.prototype = {};
 
 var Script = exports.Script = function NodeScript (code) {
@@ -53,13 +67,7 @@ Script.prototype.runInContext = function (context) {
         throw new TypeError("needs a 'context' argument.");
     }
     
-    var iframe = document.createElement('iframe');
-    if (!iframe.style) iframe.style = {};
-    iframe.style.display = 'none';
-    
-    document.body.appendChild(iframe);
-    
-    var win = iframe.contentWindow;
+    var win = context._iframe.contentWindow;
     var wEval = win.eval, wExecScript = win.execScript;
 
     if (!wEval && wExecScript) {
@@ -67,7 +75,7 @@ Script.prototype.runInContext = function (context) {
         wExecScript.call(win, 'null');
         wEval = win.eval;
     }
-    
+
     forEach(Object_keys(context), function (key) {
         win[key] = context[key];
     });
@@ -95,9 +103,6 @@ Script.prototype.runInContext = function (context) {
             defineProp(context, key, win[key]);
         }
     });
-    
-    document.body.removeChild(iframe);
-    
     return res;
 };
 
@@ -132,7 +137,12 @@ exports.createContext = Script.createContext = function (context) {
     if(typeof context === 'object') {
         forEach(Object_keys(context), function (key) {
             copy[key] = context[key];
+            copy._iframe.contentWindow[key] = context[key];
         });
     }
     return copy;
 };
+
+exports.isContext = function(sandbox){
+    return sandbox instanceof Context;
+};
diff --git a/package.json b/package.json
index dd948a2..1ce62dc 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
-  "name": "vm-browserify",
-  "version": "0.0.4",
+  "name": "vm-browserify2",
+  "version": "0.0.6",
   "description": "vm module for the browser",
   "main": "index.js",
   "repository": {
diff --git a/test/vm.js b/test/vm.js
index ea8cd31..d50fa3c 100644
--- a/test/vm.js
+++ b/test/vm.js
@@ -33,3 +33,27 @@ test('vmRunInContext', function (t) {
     vm.runInContext('var y = 1', context);
     t.deepEqual(context, { foo: 1, x: 1, y: 1 });
 });
+
+
+test('vmRunInContext with closure', function (t) {
+    t.plan(4);
+
+    var context = vm.createContext();
+
+    vm.runInContext('var x = 1', context);
+    t.deepEqual(context, { x: 1 });
+
+    vm.runInContext('function y() { return ++x; }', context);
+    var x = vm.runInContext('y()', context);
+    t.equal(x, 2);
+    t.equal(context.x, 2);
+    t.equal(typeof context.y, 'function');
+});
+
+test('isContext', function (t) {
+    t.plan(2);
+
+    var context = vm.createContext();
+    t.true(vm.isContext(context));
+    t.false(vm.isContext({}));
+});