Add type hints to tutorial and Javascript examples

- Add return type annotations and parameter
  types
 - Import necessary typing modules (Optional,
 Union, Flask, Response)
 - Improve code readability and IDE support for
   examples
 - All existing tests continue to pass

examples/tutorial/flaskr/auth.py

@@ -1,4 +1,6 @@
 import functools
+from typing import Callable, Union
+from werkzeug.wrappers import Response
 
 from flask import Blueprint
 from flask import flash
@@ -16,7 +18,7 @@ from .db import get_db
 bp = Blueprint("auth", __name__, url_prefix="/auth")
 
 
-def login_required(view):
+def login_required(view: Callable) -> Callable:
     """View decorator that redirects anonymous users to the login page."""
 
     @functools.wraps(view)
@@ -30,7 +32,7 @@ def login_required(view):
 
 
 @bp.before_app_request
-def load_logged_in_user():
+def load_logged_in_user() -> None:
     """If a user id is stored in the session, load the user object from
     the database into ``g.user``."""
     user_id = session.get("user_id")
@@ -44,7 +46,7 @@ def load_logged_in_user():
 
 
 @bp.route("/register", methods=("GET", "POST"))
-def register():
+def register() -> Union[str, Response]:
     """Register a new user.
 
     Validates that the username is not already taken. Hashes the
@@ -82,7 +84,7 @@ def register():
 
 
 @bp.route("/login", methods=("GET", "POST"))
-def login():
+def login() -> Union[str, Response]:
     """Log in a registered user by adding the user id to the session."""
     if request.method == "POST":
         username = request.form["username"]
@@ -110,7 +112,7 @@ def login():
 
 
 @bp.route("/logout")
-def logout():
+def logout() -> Union[str, Response]:
     """Clear the current session, including the stored user id."""
     session.clear()
     return redirect(url_for("index"))