More robust checking for global context and exports.

Author: andrewplummer

lib/core.js

@@ -26,13 +26,7 @@ var INSTANCE = 0x2;
 // IE8 has a broken defineProperty but no defineProperties so this saves a try/catch.
 var PROPERTY_DESCRIPTOR_SUPPORT = !!(Object.defineProperty && Object.defineProperties);
 
-// The global context. Rhino uses a different "global" keyword so
-// do an extra check to be sure that it's actually the global context.
-// istanbul ignore next
-var globalContext = typeof global !== 'undefined' && global.Object === Object ? global : this;
-
-// Is the environment node?
-var hasExports = typeof module !== 'undefined' && module.exports;
+var globalContext = getGlobal();
 
 // Whether object instance methods can be mapped to the prototype.
 var allowObjectPrototype = false;
@@ -53,6 +47,19 @@ var DefaultChainable = getNewChainableClass('Chainable');
 
 // Global methods
 
+function getGlobal() {
+  // Get global context by keyword here to avoid issues with libraries
+  // that can potentially alter this script's context object.
+  return testGlobal(typeof global !== 'undefined' && global) ||
+         testGlobal(typeof window !== 'undefined' && window);
+}
+
+function testGlobal(obj) {
+  // Note that Rhino uses a different "global" keyword so perform an
+  // extra check here to ensure that it's actually the global object.
+  return obj && obj.Object === Object ? obj : null;
+}
+
 function setupGlobal() {
   Sugar = globalContext[SUGAR_GLOBAL];
   // istanbul ignore if
@@ -73,9 +80,11 @@ function setupGlobal() {
     return Sugar;
   };
   // istanbul ignore else
-  if (hasExports) {
+  if (typeof module !== 'undefined' && module.exports) {
+    // Node or webpack environment
     module.exports = Sugar;
   } else {
+    // Unwrapped browser environment
     try {
       globalContext[SUGAR_GLOBAL] = Sugar;
     } catch (e) {