AngularJS Binding for Scala.js

Introduction

scalajs-angular aims to help developers build AngularJS based applications in type safe manner with Scala language.

To achieve this goal, it depends on Scala.js to provide bindings to core AngularJS classes and functions, as well as its own APIs to enable Scala developers to access them in more natural manner.

It's still at the very early stage of development, so the most parts of the project are subject to frequent and extensive changes.

And the bindings are by no means comprehensive or exhaustive for now, so please use it at your discretion.

How to Use

SBT Settings

Add the following lines to your sbt build definition:

libraryDependencies += "com.greencatsoft" %%% "scalajs-angular" % "0.7"

If you want to test the latest snapshot version instead, change the version to 0.8-SNAPSHOT and add Sonatype snapshot repository to the resolver as follows:

resolvers += 
  "Sonatype OSS Snapshots" at "https://oss.sonatype.org/content/repositories/snapshots"

Or more simply as,

resolvers += Resolver.sonatypeRepo("snapshots")

Defining a Module

You can define an AngularJS module in the following manner:

val module = Angular.module("myproject", Seq("ngRoute", "ui.bootstrap"))

And you can either register your Angular components like a controller either as a class, or as a singleton object like below:

// In case of registering a class
module
  .config[RoutingConfig]
  .factory[UserServiceFactory]
  .controller[UserDetailController]
  .directive[UserInfoDirective]
  .run[AppInitializer]
  .filter[UpperCaseFilter]

// In case of registering a singleton object
module
  .config(RoutingConfig)
  .factory(UserServiceFactory)
  .controller(UserDetailController)
  .directive(UserInfoDirective)
  .run(AppInitializer)
  .filter(UpperCaseFilter)

Any classes or objects which is to be registered as an Angular component should be inheriting from Service trait (or one of its subtypes, like Controller). And in case with injectable services, like controllers, factories, directives, or filters, you need to specify its name using the @injectable annotation like shown below:

@injectable("todoEscape")
class EscapeDirective extends AttributeDirective {
  ...
}

In case of a factory, both the factory itself and its product type should be annotated with @injectable using the same name:

@injectable("taskService")
class TaskService(http: HttpService) extends Service {
  ...
}

@injectable("taskService")
class TaskServiceFactory(http: HttpService) extends Factory[TaskService] {
  ...
}

Managing Dependencies

You can find core AngularJS services like HttpService or Location in the core package, while those from any third party modules reside in the extensions package.

And such dependencies can be injected into any object which inherits from the Service trait, including Controller, Directive, Factory, and more.

From 0.5 version onward, it also supports constructor based dependency injection (which was first attempted by an alternate implementation of the Angular.js API in Scala.js, scalajs-angulate) as well as the traditional property based approach.

In general, the constructor based approach should be preferred, as it adheres to the Scala's principle with using immutable properties. However, if you want to declare your Angular module as a singleton object, you need to use the property based method instead, as a singleton does not have a constructor.

Note that you can mix both types of the injection method in a single component, which might be useful if you're declaring each dependencies as separate traits, like LocationAware.

Constructor Based Dependency Injection

You can declare any dependent objects as constructor arguments of the target class you want them to be injected into:

@injectable("todoCtrl")
class TodoCtrl(scope: TodoScope, location: Location, service: TaskService)
  extends AbstractController[TodoScope](scope) {

  scope.todoItems = service.getItems()
  ...
}

Using this method, you can inject any Angular components (including your own services) into any other components, provided that they have the @injectable annotation.

As the class instantiation is handled by Angular itself, you can only include valid Angular components in your constructor argument list.

Note that the @injectable annotation need not be declared on the immediate type of an argument. For example, TodoScope in the above example inhertis from Scope trait which is annotated with @injectable("$scope"), so you don't have to declare another annotation on the TodoScope trait itself.

Property Based Dependency Injection

In case of using a Scala object as Angular component, you need to inject any dependencies as properties (variables) instead of constructor arguments.

To inject a specific dependency, you can declare a variable with the @inject annotation like the following example:

@injectable("exampleCtrl")
object ExampleController extends Controller[Scope] {

  @inject
  var location: Location = _

  @inject
  override var scope: Scope = _

  // You can assume all dependencies to be resolved 
  // after this method is invoked.
  override def initialize() {
    super.initialize()

    val url = location.absUrl + "/example"
  }
}

All injected types must have a valid @injectable annotation in one of the types in their class hierarchy as mentioned previously.

One of the notable differences from the constructor based method is that, you cannot access injected objects in the constructor block of the object because they are not available at the time of the object creation.

In order to solve this problem, the Service trait extends from Initializable which provides a method def initialized(): Unit which is invoked after all dependencies are injected to the service (like @PostConstruct in Java).

Using Controllers and Scopes

Controller is a special type of Angular service, which is used to communicate with a view template by manipulating a scope object. As such, they are usually tightly coupled with associated scope objects, so their relationship is reflected in the signature of the trait which represents Angular controllers, as Controller[A <: Scope].

Normally, you would define a scope trait and declare any properties or functions you want to access from your controller class, then write a matching controller class or an object using the name of the scope trait as the type parameter of the Controller trait (or the AbstractController class for convenience).

A typical scope would look like an example below:

trait UserScope extends Scope {

  var id: String = js.native
  var name: String = js.native
  var email: String = js.native
  var friends: js.Array[String] = js.native

  var delete: js.Function = js.native
}

Note that you cannot specify a default value for a property, or write an implementation of a function of your scope trait, since Scope inherits from js.Object and Scala.js does not support such an use case yet.

So, typically, they are initialized from a constructor block, or inside the initialize method in case of an object, as shown below:

@injectable("userDetailsCtrl")
class UserDetailsController(scope: UserScope, http: HttpService) 
  extends AbstractController[UserScope](scope) {

  val future: Future[User] = http.get("/users/john")

  future onComplete {
    case Success(user) => {
      scope.id = user.id
      scope.name = user.name
      scope.email = user.email
      scope.friends = user.friends
    }
    case Failure(t) => 
      println("An error has occured: " + t.getMessage)
  }

  scope.delete = () => userService.delete(scope.id)
}

By default, the controller instance is automatically exported to the associated scope as controller variable. So, you can access an arbitrary method after you put @JSExport annotation on the method and on the controller class which encloses it:

@JSExport
@injectable("userDetailsCtrl")
class UserDetailsController(scope: UserScope, http: HttpService) 
  extends AbstractController[UserScope](scope) {
  ...
  @JSExport
  def delete(): Unit = userService.delete(scope.id)
}

<div ng-controller="userDetailsCtrl">
  ...
  <button ng-click="controller.delete()">Delete</button>
</div>

The same rule applies to the case when you use the controller-as syntax, because you cannot directly refer to the controller instance due to a limitation in the implementation.

So, if you have declared your controller as TodoCtrl as todo for instance, you can invoke its checkAll() method with todo.controller.checkAll()(instead of todo.checkAll()).

As a final note, Controller (and Directive) provides implicit conversion from Scope to js.Dynamic via scope.dynamic method, so you can use this feature to attach arbitrary properties or functions to the scope object without declaring them first:

@injectable("userDetailsCtrl")
class UserDetailsController(scope: Scope, http: HttpService) 
  extends AbstractController[Scope](scope) {
  ...
  scope.dynamic.delete = () => userService.delete(scope.id)
}

Using Services and Factories

It is recommended to implement service facades (or business delegates) are as plain Scala objects without depending any Angular specific APIs, for the sake of cleaner separation between layers.

But if you need to inject Angular components to your service object, you might want them to be registered as an Angular service as well, using Module.service method as shown below:

@injectable("taskService")
object TaskService extends Service {

  var http: HttpService = _

  override def initialize() {
    ...
  }
}
...
module.service(TaskService)

Better still, you can rewrite the above example using Factory[A] instead:

@injectable("taskService")
class TaskService(http: HttpService) {
  ...
}

@injectable("taskService")
class TaskServiceFactory(http: HttpService) extends Factory[TaskService] {
  override def apply() = new TaskService(http)
}
...
module.factory[TaskServiceFactory]

Using Directives

To define a directive, you can declare an object which implements Directive trait.

You can also mixin such traits as ElementDirective, AttributeDirective, Requires, and so on to assign more specific behaviors to your directive implementation.

Scope related configuration can also be specified by mixing in one of InheritParentScope, UseParentScope, or IsolatedScope traits.

IsolatedScope also provides its own DSL to specify attribute bindings, as specified by AngularJS API:

@injectable("myCustomer")
class CustomerDirective extends ElementDirective 
  with TemplatedDirective with IsolatedScope {

  override val templateUrl = "my-customer-iso.html"

  bindings ++= Seq(
    "customerInfo" := "info",
    "title" :@ "",
    "close" :& "onClose"
  )
}

To implement a directive which manipulates DOM elements, you can override the link method as follows:

@injectable("currentLocation")
class LocationDirective(location: Location) extends AttributeDirective {

  override def link(
    scope: ScopeType, elems: Seq[Element], attrs: Attributes, controllers: Controller[_]) {
    val elem = elems.head.asInstanceOf[HTMLElement]

    elem.innerHTML = location.path
  }
}

Using Filters

To define a filter, you can declare an object which implements Filter[A] trait, and override the filter method to handle the actual filtering:

@injectable("upper")
class UpperCaseFilter extends Filter[String] {

  override def filter(item: String): String = item.toUpperCase
}

As with other types inheriting from the Service trait, you can inject dependencies to your filter instance using the @inject annotation, and it also provides an alternative filter method which takes additional arguments:

@injectable("upper")
class UpperCaseFilter(location: Location) extends Filter[String] {

  override def filter(item: String, args: Seq[Any]) = 
    if (location.path.endsWith(args.head.toString)) 
      item.toUpperCase
    else
      item.toLowerCase
}

Defining Routes

Defining routing rules is quite straight forward, like the following example:

class RoutingConfig(routeProvider: RouteProvider) extends Config {

  routeProvider
    .when("/", Route("/assets/templates/home.html", "Home"))
    .when("/signup", Route("/assets/templates/signup.html", "Sign up", "signupCtrl"))
    .when("/users", Route("/assets/templates/users.html", "Users", "usersCtrl"))
}

(Note that you need to 'ngRoute' in your dependency list, and angular-route.js in the html file for the above code to work)

Asynchronous Task

In order to process asynchronously calculated values in Scala, you need an implicit instance of ExecutionContext is needed in scope.

Scala.js provides its own implementation as RunNowExecutionContext, which simply resolves the submitted tasks immediately.

However, it's been deprecated since 0.6.6 and replaced by QueueExecutionContext which is truly asynchronous in nature.

It could pose a problem in the context of an Angular.js application, since it has its own lifecycle to manage the scope. For example, you might notice that changed values in a scope are not immediately visible if they are assigend asynchronously, like within onComplete clause of a Future instance.

To deal with this limitation, we provide our own version of ExecutionContext, which is based on Angular.js's `$timer service.

The simplest way to use it is to make your controller or service extend from AngularExecutionContextProvider, like shown below:

// Inject '$timeout' service and extend 'AngularExecutionContextProvider'.
@injectable("todoCtrl")
class TodoCtrl(scope: TodoScope, service: TaskServiceProxy,
  val timeout: Timeout) extends AbstractController[TodoScope](scope)
  with AngularExecutionContextProvider {

  service.findAll() onComplete {
    case Success(tasks) =>
      // This expression is executed within Angular's digest cycle.
      scope.todos = tasks.toJSArray

      update()
    case Failure(t) => handleError(t)
  }
}

Example Project

There's an example implementation of TodoMvc application as a separate project:

• https://github.com/greencatsoft/scalajs-angular-todomvc

License

This project is provided under the terms of Apache License, Version 2.0.