Use IIFE like in https://github.com/jhnns/rewire-webpack/blob/e6ae0c2…

…be0cd7d273ef272b91c2934ecf3447edf/lib/rewire.loader.js

Closes #56

lib/rewire.js

@@ -36,8 +36,20 @@ function internalRewire(parentModulePath, targetPath) {
     // We prepend a list of all globals declared with var so they can be overridden (without changing original globals)
     prelude = getImportGlobalsSrc();
 
+    // The module src is wrapped inside a self-executing function.
+    // This is necessary to separate the module src from the preceding importGlobalsSrc,
+    // because the module src can be in strict mode.
+    // In strict mode eval() can only declare vars in the current scope. In this case our setters
+    // and getters won't work.
+    // @see http://whereswalden.com/2011/01/10/new-es5-strict-mode-support-new-vars-created-by-strict-mode-eval-code-are-local-to-that-code-only/
+    // It also circumvents a problem with identical global variables and function declarations
+    // @see https://github.com/jhnns/rewire/issues/56
+    prelude += "(function () { ";
+
     // We append our special setter and getter.
     appendix = "\n" + getDefinePropertySrc();
+    // End of self-executing function
+    appendix += "})();";
 
     // Check if the module uses the strict mode.
     // If so we must ensure that "use strict"; stays at the beginning of the module.