Support localStorage for storing settings

www/js/lib/cookies.js

@@ -21,11 +21,43 @@ define([], function() {
 |*|
 \*/
 
+var storeType = testStorageSupport();
+
+// Tests for localStorage support
+function testStorageSupport() {
+  // Prefer localStorage if supported due to some platforms blocking cookies in local contexts
+  // DEV: In FF extensions, cookies are blocked since at least FF 68.6 but possibly since FF 55 [kiwix-js #612]
+  var type = 'local_storage';
+  // First test for localStorage support
+  var localStorageTest = false;
+  try {
+    localStorageTest = 'localStorage' in window && window['localStorage'] !== null;
+    // DEV: Above test returns true in IE11 running from file:// protocol, but attempting to write a key to
+    // localStorage causes an exception; so to test fully, we must now attempt to write and remove a test key
+    if (localStorageTest) {
+      localStorage.setItem('kiwixStorage', '');
+      localStorage.removeItem('kiwixStorage');
+    }
+  } catch (e) {
+    localStorageTest = false;
+    console.log('LocalStorage is not supported!');
+  }
+  // Fall back to cookie if localStorage fails
+  if (!localStorageTest) type = 'cookie';
+  console.log('Storage test: type: ' + type);
+  return type;
+}
+
 var docCookies = {
   getItem: function (sKey) {
+    if (storeType === 'cookie') {
     return unescape(document.cookie.replace(new RegExp("(?:(?:^|.*;)\\s*" + escape(sKey).replace(/[\-\.\+\*]/g, "\\$&") + "\\s*\\=\\s*([^;]*).*$)|^.*$"), "$1")) || null;
+    } else {
+      return localStorage.getItem(sKey);
+    }
   },
   setItem: function (sKey, sValue, vEnd, sPath, sDomain, bSecure) {
+    if (storeType === 'cookie') {
     if (!sKey || /^(?:expires|max\-age|path|domain|secure)$/i.test(sKey)) { return false; }
     var sExpires = "";
     if (vEnd) {
@@ -42,11 +74,18 @@ var docCookies = {
       }
     }
     document.cookie = escape(sKey) + "=" + escape(sValue) + sExpires + (sDomain ? "; domain=" + sDomain : "") + (sPath ? "; path=" + sPath : "") + (bSecure ? "; secure" : "");
+    } else {
+      localStorage.setItem(sKey, sValue);
+    }
     return true;
   },
   removeItem: function (sKey, sPath) {
+    if (storeType === 'cookie') {
     if (!sKey || !this.hasItem(sKey)) { return false; }
     document.cookie = escape(sKey) + "=; expires=Thu, 01 Jan 1970 00:00:00 GMT" + (sPath ? "; path=" + sPath : "");
+    } else {
+      localStorage.removeItem(sKey);
+    } 
     return true;
   },
   hasItem: function (sKey) {
@@ -59,11 +98,11 @@ var docCookies = {
   }
 };
 
-return {
-        getItem: docCookies.getItem,
-    	setItem: docCookies.setItem,
-    	removeItem: docCookies.removeItem,
-    	hasItem: docCookies.hasItem,
-    	keys: docCookies.keys
-    };
+  return {
+    getItem: docCookies.getItem,
+    setItem: docCookies.setItem,
+    removeItem: docCookies.removeItem,
+    hasItem: docCookies.hasItem,
+    keys: docCookies.keys
+  };
 });