How to create webworker code in Scala.js

Question

How do I create the code for a web worker using Scala.js? Looking at the documentation everything seems to produce JavaScript functions rather than top level JavaScript. The new Worker constructor seems to require top level Javascript, rather than a function within a file. So in my Scala.js code I have:

var myWorker = new Worker("worker.js");
myWorker.onmessage = (e: scala.scalajs.js.Any) =>
{
  val e1 = e.asInstanceOf[MessageEvent]
  println("Worker message recieved:" -- e1.data.toString)
}
myWorker.postMessage("")

And in the file worker.js I have

self.postMessage("from webworker");

The message is picked up and displayed in the web console as intended.

Community · Accepted Answer · 2017-05-23 12:13:49Z

5

Scala.js will indeed only ever generate non-top-level code, by design. However, you can add a bit of arbitrary JavaScript code at the beginning and/or end of the generated .js file with the scalaJSOutputWrapper sbt setting:

scalaJSOutputWrapper := ("", "example.WorkerMainObject().main();")

This would cause the generated .js file to have the specified top-level statement.

See also https://stackoverflow.com/a/34764513/1829647

edited May 23, 2017 at 12:13

CommunityBot

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answered Mar 10, 2016 at 9:56

sjrd

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3 Comments

Suma Over a year ago

The scalaJSOutputWrapper is gone since scala-js.org/news/2017/07/03/announcing-scalajs-1.0.0-M1. Can one do the same with scalaJSLinkerConfig?

sjrd Over a year ago

You don't need that anymore. You can have an actual main method since v0.6.18 or something.

Suma Over a year ago

It may sound dumb, but I still fail to understand how exactly. You mean something like in stackoverflow.com/questions/35926650/… (which was asked and answered about the same time as this)?

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