zv3/Application.scala

## Application.scala
// controllers/Application.scala
object Application extends Controller {

  def index = ActionWithAttrs { implicit request =>
    Ok(views.html.index())
  }
}

object ActionWithAttrs extends StackableAction

## index.scala.html
@(implicit request: Request[_])
@main{
  @indexHead @* content that goes in the head tag *@
} {
  @indexBody
}

## indexBody.scala.html
@import views.support.JavascriptPage
@(implicit request: Request[_])
@JavascriptPage.addNonBlockingJS("some-unique-id-for-this-script") {
  window.alert("mega kill");
}

## inlineNonBlockingJS.scala.html
@import views.support.JavascriptPage
@(implicit request: Request[_])
<script src="/javascripts/your_javascript_app.js"></script>
<script id="non-blocking" type="text/javascript">
  @defining(JavascriptPage.getNonBlockingJS()) { scripts =>
    @scripts.map { case (_, item) => @item }
  }
</script>

## JavascriptPage.scala
package views.support

import controllers.{RequestWithAttributes, AttributeKey}
import play.api.mvc.{Request, RequestHeader}
import play.twirl.api.Html

// views/support/JavascriptPage.scala
object JavascriptPage {
  case class NonBlockingJS(key: String) extends AttributeKey[Html]
  case class BlockingJS(key: String) extends AttributeKey[Html]

  def addNonBlockingJS(div: String)(jscript: Html)(implicit request: Request[_]): Unit = {
    request match {
      case i: RequestWithAttributes[_] =>
        i.set(NonBlockingJS(div), jscript)
      case _ =>
    }
  }

  // scripts that are supposed to go into the <head> tag, thus blocking scripts
  def addBlockingJS(div: String)(jscript: Html)(implicit request: Request[_]): Unit = {
    request match {
      case i: RequestWithAttributes[_] =>
        i.set(BlockingJS(div), jscript)
      case _ =>
    }
  }

  // scripts that are supposed to go before the </body> tag, non blocking scripts that is
  def getNonBlockingJS()(implicit request: Request[_]): Seq[(String, Html)] = {
    request match {
      case i: RequestWithAttributes[_] =>
        i.getAll[NonBlockingJS].toSeq.map {
          case (NonBlockingJS(div), jscript: Html) => (div, jscript)
        }
      case _ => Seq.empty
    }
  }
}

## main.scala.html
@(head: Html)(body: Html)(implicit request: Request[_])
<html>
<head>
  @head
</head>
<body>
  @body

  @inlineNonBlockingJS @* we append all of our javascript non blocking code (that were added to the Map up until this line) *@
</body>

## StackableAction.scala
package controllers

import play.api.mvc._

import scala.collection.concurrent.TrieMap
import scala.concurrent.Future
import scala.reflect.ClassTag

// Borrowed from: https://github.com/rabitarochan/Play2-ChainAction/blob/master/core/src/main/scala/com/github/rabitarochan/play2/stackableaction/StackableAction.scala
// controllers/StackableAction.scala
abstract class StackableAction extends ActionBuilder[RequestWithAttributes] with StackableFilter {

  override def filter[A](request: RequestWithAttributes[A])(f: RequestWithAttributes[A] => Future[Result]): Future[Result] = {
    f(request)
  }

  def invokeBlock[A](req: Request[A], block: RequestWithAttributes[A] => Future[Result]): Future[Result] = {
    val reqWA = new RequestWithAttributes(req, new TrieMap[AttributeKey[_], Any]())
    filter(reqWA)(block)
  }

}

trait StackableFilter {
  def filter[A](request: RequestWithAttributes[A])(f: RequestWithAttributes[A] => Future[Result]): Future[Result]
}

trait AttributeKey[A] {
  def ->(value: A): Attribute[A] = Attribute(this, value)
}

case class Attribute[A](key: AttributeKey[A], value: A) {
  def toTuple: (AttributeKey[A], A) = (key, value)
}

class RequestWithAttributes[A](request: Request[A], attributes: TrieMap[AttributeKey[_], Any]) extends WrappedRequest[A](request) {
  def get[B](key: AttributeKey[B]): Option[B] = attributes.get(key).asInstanceOf[Option[B]]
  def set[B](key: AttributeKey[B], value: B): RequestWithAttributes[A] = {
    attributes.put(key, value)
    this
  }
  def getAll[T](implicit classTag: ClassTag[T]) = {
    attributes.filterKeys {
      case p: T => true
      case _    => false
    }
  }
}
	// controllers/Application.scala
	object Application extends Controller {

	def index = ActionWithAttrs { implicit request =>
	Ok(views.html.index())
	}
	}

	object ActionWithAttrs extends StackableAction
	@(implicit request: Request[_])
	@main{
	@indexHead @* content that goes in the head tag *@
	} {
	@indexBody
	}
	@import views.support.JavascriptPage
	@(implicit request: Request[_])
	@JavascriptPage.addNonBlockingJS("some-unique-id-for-this-script") {
	window.alert("mega kill");
	}
	@import views.support.JavascriptPage
	@(implicit request: Request[_])
	<script src="/javascripts/your_javascript_app.js"></script>
	<script id="non-blocking" type="text/javascript">
	@defining(JavascriptPage.getNonBlockingJS()) { scripts =>
	@scripts.map { case (_, item) => @item }
	}
	</script>
	package views.support

	import controllers.{RequestWithAttributes, AttributeKey}
	import play.api.mvc.{Request, RequestHeader}
	import play.twirl.api.Html

	// views/support/JavascriptPage.scala
	object JavascriptPage {
	case class NonBlockingJS(key: String) extends AttributeKey[Html]
	case class BlockingJS(key: String) extends AttributeKey[Html]

	def addNonBlockingJS(div: String)(jscript: Html)(implicit request: Request[_]): Unit = {
	request match {
	case i: RequestWithAttributes[_] =>
	i.set(NonBlockingJS(div), jscript)
	case _ =>
	}
	}

	// scripts that are supposed to go into the <head> tag, thus blocking scripts
	def addBlockingJS(div: String)(jscript: Html)(implicit request: Request[_]): Unit = {
	request match {
	case i: RequestWithAttributes[_] =>
	i.set(BlockingJS(div), jscript)
	case _ =>
	}
	}

	// scripts that are supposed to go before the </body> tag, non blocking scripts that is
	def getNonBlockingJS()(implicit request: Request[_]): Seq[(String, Html)] = {
	request match {
	case i: RequestWithAttributes[_] =>
	i.getAll[NonBlockingJS].toSeq.map {
	case (NonBlockingJS(div), jscript: Html) => (div, jscript)
	}
	case _ => Seq.empty
	}
	}
	}
	@(head: Html)(body: Html)(implicit request: Request[_])
	<html>
	<head>
	@head
	</head>
	<body>
	@body

	@inlineNonBlockingJS @* we append all of our javascript non blocking code (that were added to the Map up until this line) *@
	</body>
	package controllers

	import play.api.mvc._

	import scala.collection.concurrent.TrieMap
	import scala.concurrent.Future
	import scala.reflect.ClassTag

	// Borrowed from: https://github.com/rabitarochan/Play2-ChainAction/blob/master/core/src/main/scala/com/github/rabitarochan/play2/stackableaction/StackableAction.scala
	// controllers/StackableAction.scala
	abstract class StackableAction extends ActionBuilder[RequestWithAttributes] with StackableFilter {

	override def filter[A](request: RequestWithAttributes[A])(f: RequestWithAttributes[A] => Future[Result]): Future[Result] = {
	f(request)
	}

	def invokeBlock[A](req: Request[A], block: RequestWithAttributes[A] => Future[Result]): Future[Result] = {
	val reqWA = new RequestWithAttributes(req, new TrieMap[AttributeKey[_], Any]())
	filter(reqWA)(block)
	}

	}

	trait StackableFilter {
	def filter[A](request: RequestWithAttributes[A])(f: RequestWithAttributes[A] => Future[Result]): Future[Result]
	}

	trait AttributeKey[A] {
	def ->(value: A): Attribute[A] = Attribute(this, value)
	}

	case class Attribute[A](key: AttributeKey[A], value: A) {
	def toTuple: (AttributeKey[A], A) = (key, value)
	}

	class RequestWithAttributes[A](request: Request[A], attributes: TrieMap[AttributeKey[_], Any]) extends WrappedRequest[A](request) {
	def get[B](key: AttributeKey[B]): Option[B] = attributes.get(key).asInstanceOf[Option[B]]
	def set[B](key: AttributeKey[B], value: B): RequestWithAttributes[A] = {
	attributes.put(key, value)
	this
	}
	def getAll[T](implicit classTag: ClassTag[T]) = {
	attributes.filterKeys {
	case p: T => true
	case _ => false
	}
	}
	}