merge PR#20

browserify#20
browserify@55d378a
https://github.com/browserify/vm-browserify/blob/55d378a8f04e011c3e104c00809de555c3cf2a83/index.js

Author: warren-bank

index.js

@@ -5,6 +5,7 @@ var indexOf = function (xs, item) {
     }
     return -1;
 };
+
 var Object_keys = function (obj) {
     if (Object.keys) return Object.keys(obj)
     else {
@@ -39,6 +40,9 @@ var defineProp = (function() {
     }
 }());
 
+// cached iFrame instance, re-use for each runInContext Call.
+var iFrame = null;
+
 var globals = ['Array', 'Boolean', 'Date', 'Error', 'EvalError', 'Function',
 'Infinity', 'JSON', 'Math', 'NaN', 'Number', 'Object', 'RangeError',
 'ReferenceError', 'RegExp', 'String', 'SyntaxError', 'TypeError', 'URIError',
@@ -50,59 +54,66 @@ Context.prototype = {};
 
 var Script = exports.Script = function NodeScript (code) {
     if (!(this instanceof Script)) return new Script(code);
+    if(!iFrame) {
+      iFrame = document.createElement('iframe');
+      if (!iFrame.style) iFrame.style = {};
+      iFrame.style.display = 'none';
+
+      document.body.appendChild(iFrame);
+    }
     this.code = code;
+    this.iFrame = iFrame;
 };
 
 Script.prototype.runInContext = function (context) {
     if (!(context instanceof 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 = this.iFrame.contentWindow;
+    var winOriginal = Object_keys(win);
+    var originalToRestore = [];
     var wEval = win.eval, wExecScript = win.execScript;
 
     if (!wEval && wExecScript) {
         // win.eval() magically appears when this is called in IE:
         wExecScript.call(win, 'null');
         wEval = win.eval;
     }
-    
+
     forEach(Object_keys(context), function (key) {
-        win[key] = context[key];
-    });
-    forEach(globals, function (key) {
-        if (context[key]) {
-            win[key] = context[key];
-        }
+      if(win[key] !== undefined) {
+        let restore = {
+          'key': key,
+          'value': win[key]
+        };
+        originalToRestore.push(restore);
+      }
+      win[key] = context[key];
     });
-    
+
     var winKeys = Object_keys(win);
 
     var res = wEval.call(win, this.code);
-    
+
     forEach(Object_keys(win), function (key) {
         // Avoid copying circular objects like `top` and `window` by only
         // updating existing context properties or new properties in the `win`
         // that was only introduced after the eval.
         if (key in context || indexOf(winKeys, key) === -1) {
-            context[key] = win[key];
+            if (indexOf(globals, key) === -1) context[key] = win[key];
+            else defineProp(context, key, win[key]);
         }
+
+        // delete win context of extra fields
+        if (indexOf(winOriginal, key) === -1) delete win[key];
     });
 
-    forEach(globals, function (key) {
-        if (!(key in context)) {
-            defineProp(context, key, win[key]);
-        }
+    // restore context to original field values
+    forEach(originalToRestore, function (orig) {
+      win[orig.key] = orig.value;
     });
-    
-    document.body.removeChild(iframe);
-    
+
     return res;
 };