Binding.scala: Strategy to have a defined length of a Vars

Question

This is related to binding-scala-strategy-to-avoid-too-many-dom-tree-updates

In my project scala-adapters I display log entries that are sent over a websocket.

I have no control on how many entries are sent. So if there are a lot of entries the screen freezes.

I created a ScalaFiddle to simulate that: https://scalafiddle.io/sf/kzr28tq

What is the way to restrict the length of the entries (Vars) or what is the best strategy to drop the first entry of a Vars if the maximum length is reached?

Answer 1

A couple options:

• If you don't need to keep all the data around, simply replace it in the ListBuffer: https://scalafiddle.io/sf/fsaJbkc/2

  if (entries.value.length > display)
    entries.value.remove(0, entries.value.length - display)
  entries.value += (0 to 1000).map(_=>Random.nextInt(9)).mkString("")
  

• If you do need to keep all the data around but want to display a subset, use another Binding based off the first: https://scalafiddle.io/sf/i75YiYN/2

  val displayedEntries = Binding {
    val allEntries = entries.bind
    if (allEntries.length > display)
      allEntries.drop(allEntries.length - display).toList
    else
      allEntries.toList
  }
  

No change here: entries.value += (0 to 1000).map(_=>Random.nextInt(9)).mkString("")