Check for undefined on browser globals (#462)

* Check for undefined on browser globals.

Not all environments include these globals. For example, web workers do not have global window objects.

* remove redundant global checks

src/browser.js

@@ -40,20 +40,20 @@ function useColors() {
   // NB: In an Electron preload script, document will be defined but not fully
   // initialized. Since we know we're in Chrome, we'll just detect this case
   // explicitly
-  if (window && window.process && window.process.type === 'renderer') {
+  if (typeof window !== 'undefined' && window.process && window.process.type === 'renderer') {
     return true;
   }
 
   // is webkit? http://stackoverflow.com/a/16459606/376773
   // document is undefined in react-native: https://github.com/facebook/react-native/pull/1632
-  return (document && document.documentElement && document.documentElement.style && document.documentElement.style.WebkitAppearance) ||
+  return (typeof document !== 'undefined' && document.documentElement && document.documentElement.style && document.documentElement.style.WebkitAppearance) ||
     // is firebug? http://stackoverflow.com/a/398120/376773
-    (window && window.console && (window.console.firebug || (window.console.exception && window.console.table))) ||
+    (typeof window !== 'undefined' && window.console && (window.console.firebug || (window.console.exception && window.console.table))) ||
     // is firefox >= v31?
     // https://developer.mozilla.org/en-US/docs/Tools/Web_Console#Styling_messages
-    (navigator && navigator.userAgent && navigator.userAgent.toLowerCase().match(/firefox\/(\d+)/) && parseInt(RegExp.$1, 10) >= 31) ||
+    (typeof navigator !== 'undefined' && navigator.userAgent && navigator.userAgent.toLowerCase().match(/firefox\/(\d+)/) && parseInt(RegExp.$1, 10) >= 31) ||
     // double check webkit in userAgent just in case we are in a worker
-    (navigator && navigator.userAgent && navigator.userAgent.toLowerCase().match(/applewebkit\/(\d+)/));
+    (typeof navigator !== 'undefined' && navigator.userAgent && navigator.userAgent.toLowerCase().match(/applewebkit\/(\d+)/));
 }
 
 /**