fix: allow amplitude to be imported/required during SSR (#436)

Author: seanparmelee

src/index.js

@@ -1,7 +1,7 @@
 // Entry point
 import Amplitude from './amplitude';
 
-const old = window.amplitude || {};
+const old = (typeof window !== 'undefined' && window.amplitude) || {};
 const newInstance = new Amplitude();
 newInstance._q = old._q || [];
 

src/language.js

@@ -1,6 +1,7 @@
 var getLanguage = function () {
   return (
-    (navigator && ((navigator.languages && navigator.languages[0]) || navigator.language || navigator.userLanguage)) ||
+    (typeof navigator !== 'undefined' &&
+      ((navigator.languages && navigator.languages[0]) || navigator.language || navigator.userLanguage)) ||
     ''
   );
 };

src/localstorage.js

@@ -26,7 +26,7 @@ if (BUILD_COMPAT_LOCAL_STORAGE) {
 
   if (windowLocalStorageAvailable()) {
     localStorage = window.localStorage;
-  } else if (window.globalStorage) {
+  } else if (typeof window !== 'undefined' && window.globalStorage) {
     // Firefox 2-3 use globalStorage
     // See https://developer.mozilla.org/en/dom/storage#globalStorage
     try {