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Backbone Review

Today we'll be doing a review of Backbone. This is important, because tomorrow we'll be modifying your tic-tac-toe program to use a Backbone front-end.

This review will have four sections:

  1. General Backbone review
  2. Looking back at Rolodex, and Charles' implementation
  3. Looking at a new Backbone site (this repo)
  4. Evaluating whether real sites might use Backbone

1) Backbone Components Overview

Backbone JS Architecture from http://www.slideshare.net/ronreiter/writing-html5-web-apps-using-backbonejs-and-gae

Below are the Backbone components we have focused on to build our single page applications. Each component has a brief explanation along with a link to it's documentation.

Model

Models are the component of our Backbone application which retrieves and populates the data. Models also contain our applications business logic.

Collection

Collections handle a group of related models. When initially thinking about a collection, they may seem like simply a list, but they are much more powerful. Collections are useful because they can allow you to listen for (and act on) events that occur on any model within the collection.

View

Views act as the HTML representation of your Backbone Models. Views have much more power than Views in our Rails applications. Views act as the broker between the data in our application and the HTML displayed to the user.

The two main purposes of views are:

  • Templating (rendering HTML)
  • Eventing (triggering and handling events)
Clarifications on Views

Notes on el $el and this.$:

  • el: A View's el property is it's DOM element. Every view has one and by default, unless otherwise defined, it is a div element.
  • $el: The jQuery wrapper around the View's el property. It gives you easy access to jQuery methods like show(), hide() and addClass().
  • this.$: The jQuery selector function, scoped to only search within the children of the View's DOM element. This allows you to make selector calls and be certain that you're not affecting any parts of the page outside of your View's responsibility.

You should always design your Backbone Views so that they never modify DOM elements that aren't children of el. The easiest way to make sure that your Views hold to that design is to only ever use this.$ and $el to modify the page.

Using the standard jQuery $ is acceptable if you need to read parts of the page, when you might need to get the content for a template.

Events

Events are defined inside of your Views. We can utilize three different types of events to create a truly dynamic site.

DOM Events: These are events that are triggered within our events: {} or on code in the View. These events occur when there is something directly happening in the DOM.

Custom Events: These are events which we can create ourselves by extending Backbone.Events.

Backbone Events: These are technically custom events which Backbone has created for us based on common things that we need to do in a Backbone application. These are things like add, update, and remove on models and collections.

Documentation

Backbone.model Documentation

Backbone.collection Documentation

Backbone.view Documentation

Backbone.events Documentation

Backbone built-in events

Activity: Go through the Trek application and list out each individual component. Use the diagram above to help you label each component as Model, View or Collection.

2) Rolodex Structure - Review

The point of Backbone is to provide a very intentional structure to our front-end code, so that we know where to find the code that is handling the specific functionality of our application.

With Backbone being a less opinionated library/framework, it also has less rules and conventions on how to organize your application and where you implement specific functionality.

We'll take a look at a sample Rolodex solution.

If you choose to Fork & Clone this repository..

Then you'll need to execute:

$  git fetch
$  git checkout impl

Because the solution is on the impl branch.

App.js

App.js is our starting file for execution. It creates the models & our ApplicationView to start the page.

Views

  • ApplicationView was the most arbitrary. Why is it there?
    • The ApplicationView controls the whole viewport and handles the form for creating new Contacts. It also directly manages the RolodexView instance.
  • RolodexView
    • The RolodexView manages the list of Contacts and listens for events on the collection and when individual cards are selected. When a card is selected it triggers an event which the Rolodex listens to. Then the Rolodex updates the modal to show the contact details. It also directly manages all of the ContactViews instances.
  • ContactView
    • A ContactView renders one Contact Model using an Underscore template.

Notice that our views only directly interact with DOM elements inside their areas of concern. So the Cards only change HTML within their particular <DIV> element, while the RolodexView does not interact with the form.

Likewise, when one view directly manages another view (such as with the RolodexView and its ContactViews) that view effectively delegates responsbility for some of its DOM elements to the child view. The RolodexView does not directly change the HTML within any of the <DIV> elements assigned to ContactViews.

Models

Right now our models & collections have done very little. We have used them to set defaults. Our Contact Model only stores contact information, no business logic or functions.

Models can also connect to APIs CRUD operations, provide business logic and let Views know when the data has changed with Events.

We will utilize them a lot more with Tic-Tac-Toe, and that lesson will come on Monday. Yippie!

Collections

Collections are ordered groups of Models, they normally communicate with APIs for CRUD operations and let a view know of changes with the add, update and other events.

Our Rolodex here only uses the Collection's Eventing in this application.

That Other stuff

Because our Backbone application relies on a few other libraries to get it's gear'a'grinding, we have a json file that keeps track of those libraries and will include them into our project when we run npm install.

To add more libraries, or to see which ones are already included, open the package.json file and look under "devDependencies": {}

If this process sounds familiar, it's because it's basically the same as having a gem file in rails and running 'bundle install'.

  • Webpack Webpack lets us have a local webserver to run our app, translate our latest JavaScript syntax to something the browser can understand with babel and bundle our dependencies together into a single JavaScript file.

  • Underscore When you see an _. you're dealing with an underscore function. Underscore provides a bunch or useful functions to use with Backbone, but we'll mainly focus on templating.

  • JQuery Anytime you see that money sign, you're working with a Jquery object. That Jquery object is set by referring to a CSS selector for example $('body') to select the body element of the DOM.

Questions from Homework

What parts of the page does the ApplicationView directly manage?

The ApplicationView manages the "New Contact" form.

What parts of the page does the RolodexView directly manage?

The RolodexView manages the list of contacts and the details modal. It also listens for click events to hide the modal.

What parts of the page does the ContactView directly manage?

A ContactView manages a single contact card.

Which views are rendered when the RolodexCollection has been updated?

The RolodexView and all ContactViews.

For all custom events, list the following:

  1. Which view triggers the event
  2. Which view handles/listens for the event

We'll include all events here, not just custom ones.

Event Type What Triggers What Handles/Listens
Click on Save button DOM The user ApplicationView
Click on Clear button DOM The user ApplicationView
Click on a contact card DOM The user ContactView
Click off a contact card DOM The user RolodexView
update the Rolodex Backbone Automatic Rolodex (the collection). Updates come from ApplicationView (add a contact) RolodexView
select a contact card Custom ContactView when the card is clicked RolodexView

Is anything missing from this list that you used in your version of Rolodex?

3) Looking at Trek-Backbone: How Elements Interact

Intention

Let's think about the types of applications that we have built using JavaScript thus far. Scrabble was a basic functional program, but didn't really have any front-end component that did DOM manipulation or eventing. Trek was a nice SPA that used AJAX to interact with an API and jQuery events to provide much of the functionality. These types of applications were fairly small with not a lot of features or components that were difficult to keep track of.

Let's say that Trek had 5 times as many features that were built with similar interactions with APIs and events. This would be much harder to keep track of utilizing the unstructured process we were using originally. This is where we will see the greatest use-case for utilizing Backbone as our JS library.

Setup

This repo includes a completed Backbone application version of Trek that we will refer to for these activities.

You should fork and clone this repository to follow along.

Each component is responsible for specific functionality of our application. These components rely on each other, which can quickly complicate how data flows through our application.

The below activities practice understanding how the components interact with each other.

Rendering Views

The structure of our HTML has hierarchy All HTML elements are nested inside of one other element, other than the <HTML> tag. The parent element acts as a container for it's nested child elements.

Backbone views can have the same relationship, and generally mirror the HTML's hierarchy. Some backbone views will be responsible for child views and act as a container with hierarchy over the inner-elements that are generated from those child views. For example, in the Rolodex project, the rolodex view was responsible for rendering many contact views.

With our Backbone applications, a single page will likely have many different Backbone views rendering at once.

Activity: Views Responsibility

With this activity, we will identify what sections of the DOM map to specific views.

Each of the following views should correspond to a color (or other distinct marking, like dashed lines). ex: tripView is yellow, tripListView is blue and appView is red.

On the worksheet, use that color to draw a square around all the code snippets that correspond to each of these views:

  • tripView
  • tripListView
  • appView

Once you have finished, compare your worksheet with a neighbor. Review the code together and come to a consensus.

Initial Page Load

Activity: Some of our JavaScript is run immediately when the page loads, and some of it doesn't run until the user does something. To help understand which is which and in what order various things happen, let's leave ourselves a trail of breadcrumbs to follow. We'll start by looking at what does and doesn't happen when the page is first loaded.

To do so, we'll add a log line to the top of every function in our TREK app. Each line should be of form

console.log(">>> BREADCRUMBS: #");

Where # is the order in which the log line appears when the app is started. If the function shouldn't be called when the page is first loaded, replace # with does not print. So the first line to be printed out should look like

console.log(">>> BREADCRUMBS: 1");

Did things appear in the order you expected? Did you get any does not prints? Check in with the person next to you and verify, then revise your numbering if needed.

Now change your numbering to reflect the order that functions are called when various buttons are pressed.

Tracing Events

Activity It can be difficult to figure out when functions get called when we're listening to events and there's not one line of execution to follow. Now you and your partner will be diving into the events and the functions listening to those events in this Trek App.

DOM Events

Using a whiteboard make a list of the DOM events each of the views are listening to and draw arrows to functions that the events trigger.

  • When button 'See All Trips' is clicked
  • When button 'Make Reservation' is clicked

image of a DOM Event linked to a function

Now look at the event handler functions, do they invoke other events or functions? Diagram those as well.

Backbone Events

Look at the listenTo() calls in the initialize functions. Are any of the views listening to events on other objects, such as Models, Collections or Views?

Diagram those events as well.

Check your work

Now cause the events to trigger, for example click on a trip, or add a reservation.

  • Look at the console log messages you put in earlier for the Page Load activity.
  • Did they print? Were they in the expected order? Why or why not?
  • How many events did you identify? Check with a neighbor to see if they have the same.

4) Would this be a backbone app?

For each of the following websites, take a minute or so to look over the page's design, determine whether or not it would make sense to build the site as a Backbone application, and write down your reasoning for that determination: