How to do self-referencing elements

[Christoph Dietze]

Hi there,

I wanted to put together a little demo where the onfocus handler of an input prints some message that contains the input's value.

V1

    val inputElem : HTMLInputElement = input(
      `type` := "text",
      onfocus := { (e: FocusEvent) => {
        println(s"Hi from inputElem.onfocus. value: ${inputElem.value}")
      }
      }
    ).render

However I cannot do this and the compiler complains:

[error] /Users/christoph/code/scalajs-test/src/main/scala/Main.scala:28: forward reference extends over definition of value inputElem
[error]         println(s"Hi from inputElem.onfocus. value: ${inputElem.value}")

So the problem is that inputElem is really assigned after render was called. And I am trying to access it before that. The callback in which I am accessing it actually runs later.

V2

One way to do is to declare a var and reassign it:

    var inputElem2 : HTMLInputElement = null
    inputElem2 = input(
      `type` := "text",
      onfocus := { (e: FocusEvent) => {
        println(s"Hi from inputElem2.onfocus. value: ${inputElem2.value}")
      }
      }
    ).render

V3

Another way to do it is by getting the element from the event, but I need to cast and I suppose this does not work in other situations.

    val inputElem3 = input(
      `type` := "text",
      onfocus := { (e: FocusEvent) => {
        println(s"Hi from inputElem3.onfocus. value: ${e.target.asInstanceOf[HTMLInputElement].value}")
      }
      }
    ).render

Is there a more elegant solution? Currently, I would go with version 2.

[Haoyi Li]

V1 works if you make it a lazy val

Not great, but that's Scala for you. I'd say V1 with lazy val would be the best way.

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[Christoph Dietze]

That works nicely, thanks.