Anatomy of an Ember App

Imagine we are writing a web app for a site that lets users list their properties to rent. At any given time, we should be able to answer questions about the current state like What rental are they looking at? and Are they editing it? In Ember, the answer to these questions is determined by the URL. The URL can be set in a few ways:

• The user loads the app for the first time.
• The user changes the URL manually, such as by clicking the back button or by editing the address bar.
• The user clicks a link within the app.
• Some other event in the app causes the URL to change.

No matter how the URL gets set, the first thing that happens is that the Ember router maps the URL to a route handler.

The route handler then typically does two things:

• It loads a model.
• It renders a template, which has access to the model.

Models represent persistent state.

For example, a property rentals application would want to save the details of a rental when a user publishes it, and so a rental would have a model defining its details, perhaps called the rental model. You may also need a user model to keep track of who is currently logged in.

A model typically persists information to a web server, although models can be configured to save to anywhere else, such as the browser's Local Storage.

By default new Ember apps include EmberData, which is a separate data library that integrates with Ember and provides a solid, conventional model layer. We'll see EmberData in action in the tutorial in the next section.

You can also provide your own model layer using other data libraries such as Redux or Apollo, or create your own model layer using the tools that Ember provides for state, such as autotracking. We'll learn more about these tools throughout the guides.

Ember uses templates to build up the user interface in an application.

If you have written HTML before, you already know how to write a basic Ember template. For example:

<div>Hi, this is a valid Ember template!</div>

In addition to static HTML content, Ember uses the syntax of Handlebars to describe dynamic user interface elements.

For example, as mentioned before, the route handler makes the model available to its template:

{{!-- The model for this route is the current user --}}

<div>
  Hi <img src="{{@model.profileImage}}" alt="{{@model.name}}'s profile picture"> {{@model.name}},
  this is a valid Ember template!
</div>

{{#if @model.isAdmin}}
  <div>Remember, with great power comes great responsibility!</div>
{{/if}}

This example combines several Handlebars features to create a personalized experience for the user, something we couldn't do with just static HTML alone. We used the comment syntax ({{!-- ... --}}) to leave a note for future developers, the double curly braces syntax ({{...}}) to include dynamic values, as well as using the {{#if}}...{{/if}} syntax to conditionally render some extra content.

We will go into more details about each of these template features later on in this guide.

Components allow you to break up your templates and organize them into small, self-contained and reusable pieces.

In its most basic form, a component is just a piece of template that can be referred to by name. Similar to functions in programming languages, they can also take arguments, allowing them to be customized to the specific context they are being rendered into.

For example, the example in the previous section is getting a bit long. We can extract the snippet for rendering the user's name and profile picture into its own component:

<img src="{{@user.profileImage}}" alt="{{@user.name}}'s profile picture"> {{@user.name}}

Doing this allows us to simplify the original template like so:

{{!-- The model for this route is the current user --}}

<div>
  Hi <UserProfile @user={{@model}} /> this is a valid Ember template!
</div>

{{#if @model.isAdmin}}
  <div>Remember, with great power comes great responsibility!</div>
{{/if}}

Not only did we clean up the original template to be more readable, we now have a <UserProfile> component that we can reuse whenever we need to render information about a given user.

You can think of components as Ember's way for letting you create your own HTML tags. In addition to rendering content, components can also have JavaScript code associated with them, allowing you to add behavior, such as responding to a user clicking on your component.

We will cover these advanced component features in a later chapter. For now, let's see these core concepts in action by building a property rental application in the next lesson.