A walkthrough of how to write a complete HTML5 web app (both front end and back end) using Google App Engine (Python), Backbone.js, Require.js, underscore.js and jQuery.

1. Writing HTML5 Web Apps
Google App Engine
Backbone.js
Require.js
jQuery
Ron Reiter © 2012

2. Agenda
 Why do you need to learn how to program HTML5 web
apps?
 A walkthrough over the To-Do list anatomy
 https://github.com/ronreiter/webapp-boilerplate

3. Why?
 Web Apps = Software as a Service
 Cross OS/platform/browser
 Cuts costs on deployment and maintenance
 Scales easily
 Google App Engine, Amazon, Heroku, etc.
 Mobile Apps
 Cross device development cuts development costs
 WebView
 PhoneGap

4. Brief Introduction
 Google App Engine - Solid, scalable server framework
 Platform as a Service
 Backbone.js - Proven MVC framework
 LinkedIn mobile, Foursquare, Do.com, Groupon, Posterous,
Basecamp mobile, Kicksend, etc...
 Require.js - Modular JavaScript Loader
 Module dependency management
 JavaScript minification & bundling
 jQuery - DOM Manipulation Framework
 Creating dynamic content and replacing Flash

5. The To-Do List

6. Web App Architecture
Front End
Backbone.js
REST API
Back End
Google App Engine

7. Back-End

8. Dataset
 We want to create a Todo list item table.
 Start by adding a Google App Engine model
# the Todo model.
class Todo(db.Model):
content = db.StringProperty()
done = db.BooleanProperty()
order = db.IntegerProperty()

9. Request Handler
 Serves all web requests
 We implement a main handler and REST API
def main():
application = webapp.WSGIApplication([
# index.html
('/', MainHandler),
# REST interface
('/todos', TodoListHandler),
('/todos/(d+)', TodoItemHandler),
], debug=True)
util.run_wsgi_app(application)

10. Main Request Handler
 When we access http://www.todolist.com, the app is
downloaded to our computer and starts to run.
class MainHandler(webapp.RequestHandler):
def get(self):
self.response.out.write(
template.render("index.html", {}))

11. REST API Standard
 REST API is used to let clients control datasets, using four
CRUD operations:
 Create a new item – using HTTP POST requests
 Read a list of items – using HTTP GET requests
 Update a single item – using HTTP PUT requests
 Delete a single item – using HTTP DELETE requests
 Similar to SQL, but this is a customized interface and not a
way to access a database
 REST API uses XML or JSON serialization (Javascript Object
Notation) to encode and decode objects
 We’ll use JSON

12. REST API – GET (get all tasks)
class TodoListHandler (webapp.RequestHandler):
def get(self):
# serialize all Todos,
# include the ID in the response
todos = []
for todo in Todo.all():
todos.append({
"id" : todo.key().id(),
"content" : todo.content,
"done" : todo.done,
"order" : todo.order,
})
# send them to the client as JSON
self.response.out.write(simplejson.dumps(todos))

13. REST API – POST (add a new task)
class TodoListHandler (webapp.RequestHandler):
def post(self):
data = simplejson.loads(self.request.body) # load JSON data of the object
todo = Todo(
content = data["content"],
done = data["done"],
order = data["order"],
).put() # create the todo item
# send it back, and include the new ID.
self.response.out.write(simplejson.dumps({
"id" : todo.id(),
"content" : data["content"],
"done" : data["done"],
"order" : data["order"],
}))

14. REST API – PUT (update a task)
class TodoItemHandler (webapp.RequestHandler):
def put(self, id):
data = simplejson.loads(self.request.body) # load the updated model
todo = Todo.get_by_id(int(id)) # get it model using the ID from the request path
todo.content = data["content"]
todo.done = data["done"]
todo.order = data["order"]
todo.put() # update all fields and save to the DB
# send it back using the updated values
self.response.out.write(simplejson.dumps({
"id" : id,
"content" : todo.content,
"done" : todo.done,
"order" : todo.order,
}))

15. REST API – DELETE (delete a task)
class TodoItemHandler (webapp.RequestHandler):
def delete(self, id):
# find the requested model and delete it.
todo = Todo.get_by_id(int(id))
todo.delete()

16. Front-End

17. Backbone.js Architecture – MVC
Server Model Database
Backbone REST Sync
Model View
Backbone.Model HTML + CSS
DOM Manipulation
With jQuery and
templating
Controller
Backbone.View View Events
Model Events

18. Backbone.js Architecture – REST Sync
Collection Operations Collection Model Operations
GET /tasks PUT /tasks/38
POST /tasks View Model DELETE /tasks/38
PUT /tasks/39
View Model DELETE /tasks/39
PUT /tasks/40
View Model DELETE /tasks/40
PUT /tasks/41
View Model DELETE /tasks/41

19. Web App Directory Structure
 index.html – Main entry point
 css
 todos.css – Defines the style
 js
 libs
 require.js, jQuery, Backbone, Underscore
 models
 todo.js – The todo item model
 collections
 todos.js – The todo item collection
 views
 todos.js – The todo item view
 App.js – The app view
 templates
 stats.html
 todo.html – The todo item template
 main.js – Require.js entry point

20. index.html
 Loads the stylesheet
<link
rel="stylesheet"
href="css/todos.css”/>
 Loads the main.js script
<script
data-main="js/main"
src="js/libs/require/require.js">
</script>

21. main.js
 Configures paths and known libraries
 text is used for require.js text loading (for templates)
require.config({
paths: {
jquery: 'libs/jquery/jquery-min',
underscore: 'libs/underscore/underscore-min',
backbone: 'libs/backbone/backbone-optamd3-min',
text: 'libs/require/text'
}
});

22. main.js – cont.
 Load the app view (views/app.js)
 Notice there is no need to add the JS extension
 Require.js supplies us with a function to run Javascript
code only after certain modules have been loaded.
 This allows us to create a dependency model, and a new
way to write Javascript modules.
require(['views/app'], function(AppView){
var app_view = new AppView;
});

23. views/app.js – The AppView
 Backbone's "View" is actually a "View Controller". The view
itself is the template combined with CSS.
 Creating a new view either means
 creating a new DOM element using JavaScript/jQuery or
templating
 Using an existing one in the DOM
 Since there is only one app, we’ll use an existing element
for the AppView.
 However, task views are more dynamic, and they will
create new DOM elements.

24. views/app.js – The AppView (cont.)
 The define function allows us to depend on
libraries, template files and other modules we wrote.
 Every dependency in the list corresponds to an argument
of the function to execute once all modules are loaded.
define([
'jquery’, 'underscore', 'backbone',
'collections/todos’, 'views/todos',
'text!templates/stats.html'
], function($, _, Backbone,
Todos, TodoView, statsTemplate) {
var AppView = Backbone.View.extend({ ...

25. views/app.js – The AppView (cont.)
 The "View" captures and delegates events on DOM
elements
events: {
"keypress #new-todo": "createOnEnter",
"click .todo-clear a": "clearCompleted”
},

26. views/app.js – The AppView (cont.)
 We add some handlers on the Todos collection to get
notified when it's updated.
 Then, we fetch the Todos collection from the server.
 Once the data is loaded, addAll will be executed.
initialize: function() {
Todos.bind('add', this.addOne);
Todos.bind('reset', this.addAll);
Todos.fetch();
},

27. collections/todos.js – Todo Collection
 Backbone Collections are model arrays which synchronize with the server.
 The AppView listens for changes on this collection, and can add new models to it.
define([
'underscore', 'backbone', 'models/todo’
], function(_, Backbone, Todo){
var TodosCollection = Backbone.Collection.extend({
model: Todo,
url: '/todos',
done: function() {
return this.filter(function(todo){
return todo.get('done');
});
}
});

28. models/todo.js – Todo Model
 Holds the Todo item data
 Defines the default values and methods related to the data
 The "define" function needs to return the model class. When
"model/todo" will be required, it will be received.
define(['underscore', 'backbone'], function(_, Backbone) {
var TodoModel = Backbone.Model.extend({
defaults: { content: "empty todo...”, done: false, order: 0 }
});
return TodoModel;
});

29. views/todos.js – Todo View
 Bind the view to the model
 Render function uses the model data to render the template
define(['jquery', 'underscore', 'backbone’, 'models/todo',
'text!templates/todos.html'
], function($, _, Backbone, Todo, todosTemplate){
var TodoView = Backbone.View.extend({
model: Todo,
template: _.template(todosTemplate),
initialize: function() {
this.model.bind('change', this.render);
this.model.bind('destroy', this.remove);
},
render: function() {
$(this.el).html(this.template(this.model.toJSON()));
...

30. views/todos.js – Todo View
(cont.)
 Manipulate the view's model according to triggered events
events: {
"click .check" : "toggleDone",
...
}
// Toggle the "done" state of the model.
toggleDone: function() {
this.model.save({done : !this.model.get("done")});
},

31. templates/todos.html
 Template files are used to build the views either:
 Once (and then update using jQuery)
 On every update (if you're lazy)
 Use <%- ... -> for escaping HTML
<div class="todo <%= done ? 'done' : '' %>">
<div class="display">
<input class="check"
type="checkbox" <%= done ? 'checked="checked"' : '' %> />
<div class="todo-content"><%- content %></div>
<span class="todo-destroy"></span>
</div>
<div class="edit">
<input class="todo-input" type="text" value="<%- content %>" />
</div>
</div>

32. Questions?