The document discusses Korolev, a Scala library for building single-page applications that run entirely on the server. It allows moving heavy computations from the client to the server for faster page loads and a classic web development experience while maintaining reactive user interfaces. State is managed on the server and rendered markup is sent to the browser. Potential issues include high garbage collection load and latency for distant users, but the next steps are to complete the library, stabilize its API, and recruit new contributors.

1. Single-page
apps running
on server
Aleksey Fomkin
Data Monsters

2. Korolev
(in honor of Sergey Korolev, man who launch
Yuri Garagin to the space.)

3. What is that?
1. Modern single-page apps
2. Everything runs on server
3. Scala, Functional

4. Motivation
1. Move heavy computations from client
2. Instant page loading
3. Achieve classic web development experience,
keeping reactive user experience

5. Server Client
State
Virtual DOM Change Set
Bridge
Browser DOM
User ActionsTransition

6. State
case class Todo(
text: String,
done: Boolean
)
case class State(todos: Vector[Todo])

7. Transition
def todoClick(i: Int): Transition[State] = { case state =>
val updatedTodo = state.todos(i).copy(done = !todo.done)
val updatedTodos = state.todos.updated(i, updatedTodo)
state.copy(todos = updated)
}
type Transition[S] = PartialFunction[S, S]

8. Transition
def addTodo(todo: Todo): Transition[State] = {
case state =>
state.copy(todos = state.todos :+ todo)
}

9. Render
def render: Render[State] = { case state =>
state.todos map { todo =>
'div(
'input('type /= "checkbox", 'checked when todo.done),
if (!todo.done) 'span(todo.text)
else 'strike(todo.text)
)
}
}

10. Lets try?

11. Source code of demo
https://github.com/fomkin/korolev-demo-fpconf

12. Possible problems
1. High GC load
2. High latency for users who located too far from
DC

13. Next steps
1. Make library feature complete
2. API stabilization
3. New contributors

14. Thanks!
Questions?
Aleksey Fomkin
aleksey.fomkin@gmail.com
https://github.com/fomkin/korolev