When I use scala.js to write scala code to generate javascript, I found it difficult sometimes to wrap the 3rd-party javascript code into scala objects.
Is there anyway to embed some javascript code directly? e.g. as strings?
When I use scala.js to write scala code to generate javascript, I found it difficult sometimes to wrap the 3rd-party javascript code into scala objects.
Is there anyway to embed some javascript code directly? e.g. as strings?
Share Improve this question asked Feb 22, 2015 at 9:03 FreewindFreewind 198k163 gold badges452 silver badges733 bronze badges1 Answer
Reset to default 20No, there isn't, on purpose. How would identifiers in the "embedded" JavaScript code bind to identifiers in the surrounding Scala.js code, for example? That would never make any sense.
The ugly workaround: js.eval
You can "embed" JavaScript code as a parameter to the js.eval function, obviously.
import scala.scalajs.js
def foo(x: Int): Unit =
js.eval("console.error('hello');")
But js.eval always evaluates in the global scope (not in the scope where you call it), so this doesn't work:
def foo(x: Int): Unit =
js.eval("console.error(x);") // x undefined here
The good solution: js.Dynamic
Although you cannot embed arbitrary JavaScript code in Scala.js code, you can use js.Dynamic and js.DynamicImplicits. With those, you can typically transliterate JavaScript code directly into Scala syntax (which is very close to JS syntax) with the "JavaScript semantics":
import scala.scalajs.js
import js.DynamicImplicits._
import js.Dynamic.{global => g}
def foo(x: Int): Unit =
g.console.error(x)
You can even write crazy JavaScript-ish code like this:
if (g.console)
(g.console.error || g.console.log).call(g.console, x)
if you want to be robust against console or console.error not existing, for example.
The advantage of this approach is that normal binding rules for identifiers. And you don't have to resort to strings to get the job done.