Modified some FileSystem APIs as per the review documents.

FileSystem/file_system.d.ts

@@ -102,16 +102,16 @@ export declare class Folder extends FileSystemEntity {
 /**
   * Provides access to the top-level Folders instances that are accessible from the application. Use these as entry points to access the FileSystem.
   */
-export declare class KnownFolders {
+export declare module knownFolders {
     /**
     * Gets the Documents folder available for the current application. This Folder is private for the application and not accessible from Users/External apps.
     */
-    public static documents(): Folder;
+    export function documents(): Folder;
 
     /**
     * Gets the Temporary (Caches) folder available for the current application. This Folder is private for the application and not accessible from Users/External apps.
     */
-    public static temporary(): Folder;
+    export function temp(): Folder;
 }
 
 /**

FileSystem/file_system.ts

@@ -29,12 +29,12 @@ var createFile = function (info: { path: string; name: string; extension: string
 };
 
 var createFolder = function (info: { path: string; name: string; }) {
-    var documents = KnownFolders.documents();
+    var documents = knownFolders.documents();
     if (info.path === documents.path) {
         return documents;
     }
 
-    var temp = KnownFolders.temporary();
+    var temp = knownFolders.temp();
     if (info.path === temp.path) {
         return temp;
     }
@@ -48,8 +48,8 @@ var createFolder = function (info: { path: string; name: string; }) {
 };
 
 /**
-    * Represents the basic file system entity - a File or a Folder.
+* Represents the basic file system entity - a File or a Folder.
-    */
+*/
 export class FileSystemEntity {
     /**
     * Gets the Folder object representing the parent of this entity. Will be null for a root folder like Documents or Temporary.
@@ -160,6 +160,7 @@ export class File extends FileSystemEntity {
 
         return createFile(fileInfo);
     }
+
     /**
         * Checks whether a File with the specified path already exists.
         */
@@ -174,6 +175,7 @@ export class File extends FileSystemEntity {
         this.checkAccess();
         return new FileReader(this);
     }
+
     /**
         * Creates a FileWriter object over this file and locks the file until the writer is released.
         */
@@ -181,12 +183,14 @@ export class File extends FileSystemEntity {
         this.checkAccess();
         return new FileWriter(this);
     }
+
     /**
         * Gets the extension of the entity.
         */
     get extension(): string {
         return this[extensionProperty];
     }
+
     /**
         * Gets a value indicating whether the file is currently locked, meaning a background operation associated with this file is running.
         */
@@ -204,8 +208,8 @@ export class File extends FileSystemEntity {
 }
 
 /**
-    * Represents a Folder entity.
+* Represents a Folder entity.
-    */
+*/
 export class Folder extends FileSystemEntity {
     /**
     * Attempts to access a Folder at the specified path and creates a new Folder if there is no existing one.
@@ -315,44 +319,44 @@ export class Folder extends FileSystemEntity {
 }
 
 /**
-    * Provides access to the top-level Folders instances that are accessible from the application. Use these as entry points to access the FileSystem.
+* Provides access to the top-level Folders instances that are accessible from the application. Use these as entry points to access the FileSystem.
-    */
+*/
-export class KnownFolders {
+export module knownFolders {
-    private static _documents: Folder;
+    var _documents: Folder;
-    private static _temp: Folder;
+    var _temp: Folder;
 
     /**
     * Gets the Documents folder available for the current application. This Folder is private for the application and not accessible from Users/External apps.
     */
-    public static documents(): Folder {
+    export var documents = function (): Folder {
-        if (!KnownFolders._documents) {
+        if (!_documents) {
             var path = getFileAccess().getDocumentsFolderPath();
-            KnownFolders._documents = new Folder();
+            _documents = new Folder();
-            KnownFolders._documents[pathProperty] = path;
+            _documents[pathProperty] = path;
-            KnownFolders._documents[isKnownProperty] = true;
+            _documents[isKnownProperty] = true;
         }
 
-        return KnownFolders._documents;
+        return _documents;
-    }
+    };
 
     /**
     * Gets the Temporary (Caches) folder available for the current application. This Folder is private for the application and not accessible from Users/External apps.
     */
-    public static temporary(): Folder {
+    export var temp = function (): Folder {
-        if (!KnownFolders._temp) {
+        if (!_temp) {
             var path = getFileAccess().getTempFolderPath();
-            KnownFolders._temp = new Folder();
+            _temp = new Folder();
-            KnownFolders._temp[pathProperty] = path;
+            _temp[pathProperty] = path;
-            KnownFolders._temp[isKnownProperty] = true;
+            _temp[isKnownProperty] = true;
         }
 
-        return KnownFolders._temp;
+        return _temp;
     }
 }
 
 /**
-    * Base class for FileReader and FileWriter APIs.
+* Base class for FileReader and FileWriter APIs.
-    */
+*/
 export class FileAccess {
     private _file;
 
@@ -378,8 +382,8 @@ export class FileAccess {
 }
 
 /**
-    * Enables reading the content of a File entity.
+* Enables reading the content of a File entity.
-    */
+*/
 export class FileReader extends FileAccess {
     /**
     * Reads the content of the underlying File as a UTF8 encoded string.
@@ -390,8 +394,8 @@ export class FileReader extends FileAccess {
 }
 
 /**
-    * Enables saving data to a File entity.
+* Enables saving data to a File entity.
-    */
+*/
 export class FileWriter extends FileAccess {
     public writeText(content: string, onSuccess?: () => any, onError?: (error: any) => any) {
         getFileAccess().writeText(this.file.path, content, onSuccess, onError);

FileSystem/file_system_access.android.ts

@@ -349,7 +349,8 @@ export class FileSystemAccess {
     private getFileExtension(path: string): string {
         var dotIndex = path.lastIndexOf(".");
         if (dotIndex && dotIndex >= 0 && dotIndex < path.length) {
-            return path.substring(dotIndex);
+            // return the extension without the "." (like in iOS)
+            return path.substring(dotIndex + 1);
         }
 
         return undefined;