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This presentation has been developed in the context of the Mobile Applications Development course, DISIM, University of L'Aquila (Italy), Spring 2014.

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  1. 1. Gran Sasso Science Institute Ivano Malavolta Backbone JS
  2. 2. Roadmap •  Why Backbone •  Events •  Models •  Collections •  Views •  Routers •  Summary
  3. 3. Why Backbone We are building apps, not web sites If your code is not structured: •  it is extremely easy that your web app becomes a big mess of HTML + CSS + JavaScript •  maintaining each part of your app asks for a deep analysis of ALL its aspects (logic, presentation, etc.) •  you may waste a whole day due to a missing  <  
  4. 4. Why Backbone Backbone gives you STRUCTURE
  5. 5. What we want to avoid Imagine yourself trying to change •  how a movie should be rendered in your app •  the REST API providing info about movies
  6. 6. Why Backbone From the Backbone website... manipulate the DOM lists of models represent data
  7. 7. Why Backbone Additionally, Backbone provides also features for: sync for managing how to persist models (default is via REST) events for managing how data and control are exchanged within your app router for managing the interaction flow among views
  8. 8. Who is using Backbone?
  9. 9. Roadmap •  Why Backbone •  Events •  Models •  Collections •  Views •  Routers •  Summary
  10. 10. Events Any object communicates with other objects via events It gives the object the ability to bind and trigger custom named events It is extremely useful for exchanging data and control among objects
  11. 11. Events Basically, each object can: •  listen to events •  trigger events
  12. 12. Events Two types of events: you define your own types of event built-in custom
  13. 13. Events API object will react to the “alert” event (the “off” function detaches the event) event parameters the “alert” event is fired
  14. 14. Events API Events methods: on object.on(event, callback, [context]) off[event], [callback], [context]) once object.once(event, callback, [context]) trigger object.trigger(event, [*args]) listenTo object.listenTo(other, event, callback) stopListening object.stopListening([other], [event], [callback]) listenToOnce object.listenToOnce(other, event, callback)
  15. 15. Events summary
  16. 16. Roadmap •  Why Backbone •  Events •  Models •  Collections •  Views •  Routers •  Summary
  17. 17. Models Models represent your data Each model represents a data type in your app, together with the logic surrounding it, like: •  persistence •  conversions •  validation •  computed properties •  access control MVC: Notify their observers about state using the Observer pattern
  18. 18. Models You extend Backbone.Model with your domain-specific methods, and Model provides a basic set of functionality for managing changes, like: •  getter and setter •  id •  constructor •  REST-based persistence
  19. 19. Example of model custom method g an attribute event fired when “color” changes custom method invocation
  20. 20. Model constructor and attributes initialize() it is triggered every time you create a new instance of a model it works also for collections and views it can take a JS object for setting also attributes get() & set() they are used to set and retrieve the value of certain attributes defaults a property named 'defaults' in your model declaration
  21. 21. Example
  22. 22. Model persistence Backbone.sync is the function that Backbone calls every time it attempts to read or save a model By default, it uses Ajax to make a REST-ish request to a server Resources represented as JSON strings
  23. 23. Sync signature sync(method,  model,  [options])   method the CRUD method ("create“, "read“, "update", or "delete") model the model (or collection) to be synced options success and error callbacks, and all other jQuery request options example of overriden sync: Sync returns a jQuery XMLHttpRequest (jqXHR) object It implements the Promise interface
  24. 24. Sync usage Normally you will not use the sync method directly, you will do it implicitly when you call one of these methods Model •  fetch: gets the most up-to-date values of the model instance •  save: persists the model instance •  destroy: deletes the model instance Collection •  fetch: gets all the models of the collection from the server •  create: creates a model, saves it to the server and adds it to the collection
  25. 25. Overriding sync You can override it in order to use a different persistence strategy, such as: •  WebSockets •  Local Storage •  WebSQL Backbone.sync is the default global function that all models use unless the models have a sync method specifically set
  26. 26. Models summary
  27. 27. Roadmap •  Why Backbone •  Events •  Models •  Collections •  Views •  Routers •  Summary
  28. 28. Collections Collections are ordered sets of models You can: •  bind change events to be notified when any model in the collection has been modified •  listen for add and remove events •  fetch the collection from the server (or other persistence layers) •  find models or filter collections themeselves The model attribute of a collection represents the kind of model that can be stored in it Any event that is triggered on a model in a collection will also be triggered on the collection directly MVC: Notify their observers about state using the Observer pattern (same as models)
  29. 29. Collection example
  30. 30. Collections summary
  31. 31. Roadmap •  Why Backbone •  Events •  Models •  Collections •  Views •  Routers •  Summary
  32. 32. Views Views represent and manage the visible parts of your application They are also used to •  listen to interaction events •  and react accordingly views can be rendered at any time, and inserted into the DOM you get high-performance UI rendering with as few reflows and repaints as possible MVC: observe models, and update itself according to the state of the models + manage user inputs (it’s a controller, to this sense)
  33. 33. Interaction with the DOM All views refer to a DOM element at all times, even if they are already in the page or not   this.el is a reference to the DOM element, it is created from: tagName for example body,  ul,  span,  img   className class name of some element within the DOM id id of an element within the DOM If none of them is specified, this.el is an empty <div>
  34. 34. Rendering the view The render() method is used to update the this.el element with the new HTML The default implementation of render() is a no-op à you have to override it to update this.el with your HTML code Backbone is agnostic with respect to your code in render(), however... you are STRONGLY encouraged to use a JavaScript templating library here
  35. 35. View example
  36. 36. Interaction with the user Events map “event_name selector”: callback Events callbacks
  37. 37. Views summary
  38. 38. Roadmap •  Why Backbone •  Events •  Models •  Collections •  Views •  Routers •  Summary
  39. 39. The router Backbone.Router  provides methods for routing client-side pages, and connecting them to actions and events At a minimum, a router is composed of two main parts: routes an hash that pairs routes to actions actions JS functions triggered when certain routes are navigated
  40. 40. Routing Every router contains an hash that maps routes to functions on your router URLs fragments can also contain dynamic data via Backbone-specific URL parts: parameter  (:param)   match a single URL component between slashes splat  (*fragment)   match any number of URL components
  41. 41. Routing routes map routing functions
  42. 42. History History serves as a global router to 1.  handle hashchange events 2.  match the appropriate route 3.  trigger callbacks You should never access it directly, you just need call Backbone.history.start()  to begin monitoring hashchange events, and dispatching routes in your app Call Backbone.history.navigate(ROUTE_NAME,  {trigger:  true}); to activate a specific route of the router   Technically, it uses the HTML5 History API to listen to to its job For older browsers, it uses URL hash fragments as fallback
  43. 43. Router summary
  44. 44. Roadmap •  Why Backbone •  Events •  Models •  Collections •  Views •  Routers •  Summary
  45. 45. Classical workflow 1.  You dig into JSON objects 2.  Look up elements in the DOM 3.  Update the HTML by hand
  46. 46. Backbone-based workflow •  You organize your interface into logical views backed by models •  Each view can be updated independently when the model changes, without having to redraw the page You can bind your view‘s render() function to the model‘s "change” event à now everywhere that model data is displayed in the UI, it is always immediately up to date
  47. 47. Is Backbone real MVC? Let’s look at the description of the Model-View-Presenter pattern on Wikipedia: an interface defining the data to be displayed or otherwise acted upon in the user interface passive interface that displays data (the model) and routes user commands (events) to the presenter to act upon that data acts upon the model and the view. It retrieves data from repositories (the model), and formats it for display in the view Model View Presenter
  48. 48. References
  49. 49. + 39 380 70 21 600 Contact Ivano Malavolta | Gran Sasso Science Institute iivanoo