Writing HTML5 Web Apps using Backbone.js and GAE

Writing HTML5 Web Apps

Google App Engine

Backbone.js

Require.js

jQuery

Ron Reiter © 2012

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

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

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

Web App Architecture

Front End
Backbone.js

REST API

Back End
Google App Engine

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()

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)

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", {}))

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

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))

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"],
}))

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,
}))

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()

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

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
PUT /tasks/41

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

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>

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'
}
});

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;
});

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.

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({ ...

 The "View" captures and delegates events on DOM
elements

events: {
"keypress #new-todo": "createOnEnter",
"click .todo-clear a": "clearCompleted”
},

 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();
},

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');
});
}
});

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;
});

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()));
...

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")});
},

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>

Writing HTML5 Web Apps using Backbone.js and GAE

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