add script to fallback localStorage to cookie, using https://stackoverflow.com/a/12302790/1428034

static/local-storage-polyfill.js

@@ -0,0 +1,76 @@
+// From https://stackoverflow.com/a/12302790/1428034
+window.store = {
+  localStoreSupport: function () {
+    try {
+      return 'localStorage' in window && window['localStorage'] !== null;
+    } catch (e) {
+      return false;
+    }
+  },
+  set: function (name, value, days) {
+    if (days) {
+      var date = new Date();
+      date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
+      var expires = "; expires=" + date.toGMTString();
+    }
+    else {
+      var expires = "";
+    }
+    if (this.localStoreSupport()) {
+      localStorage.setItem(name, value);
+    }
+    else {
+      document.cookie = name + "=" + value + expires + "; path=/";
+    }
+  },
+  get: function (name) {
+    if (this.localStoreSupport()) {
+      var ret = localStorage.getItem(name);
+      //console.log(typeof ret);
+      switch (ret) {
+        case 'true':
+          return true;
+        case 'false':
+          return false;
+        default:
+          return ret;
+      }
+    }
+    else {
+      // cookie fallback
+      /*
+       * after adding a cookie like
+       * >> document.cookie = "bar=test; expires=Thu, 14 Jun 2018 13:05:38 GMT; path=/"
+       * the value of document.cookie may look like
+       * >> "foo=value; bar=test"
+       */
+      var nameEQ = name + "=";  // what we are looking for
+      var ca = document.cookie.split(';');  // split into separate cookies
+      for (var i = 0; i < ca.length; i++) {
+        var c = ca[i];  // the current cookie
+        while (c.charAt(0) == ' ') c = c.substring(1, c.length);  // remove leading spaces
+        if (c.indexOf(nameEQ) == 0) {  // if it is the searched cookie
+          var ret = c.substring(nameEQ.length, c.length);
+          // making "true" and "false" a boolean again.
+          switch (ret) {
+            case 'true':
+              return true;
+            case 'false':
+              return false;
+            default:
+              return ret;
+          }
+        }
+      }
+      return null; // no cookie found
+    }
+  },
+  del: function (name) {
+    if (this.localStoreSupport()) {
+      localStorage.removeItem(name);
+    }
+    else {
+      this.set(name, "", -1);
+    }
+  },
+}