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Global Config

Compile-Time Settings: Limitations

There's currently a limitation that components use the compile-time settings available when they're compiled. Seems like a pretty obvious way to go so why is it a limitation? When you're writing components in your app (which is what the vast majority of us do), then this isn't a limitation and it will work the way you expect. On the other hand, if you're writing components in a library, the library author's settings are used, and downstream users (currently) don't have a way to recompile it with their own settings. This may (and should) change in the future. If this is important to you or your organisation, feel free to reach out and sponsor the required work.

Compile-Time Settings: Usage

First add this to your sbt:

scalacOptions ++= // Required since sbt 1.6.0
  sys.props.iterator
    .filter(_._1.contains("japgolly"))
    .map(x => s"-D${x._1}=${x._2}")
    .toSeq

Currently, you have to specify compile-time settings to sbt directly when you start it.

Examples:

# Format:
sbt \
 -D<key1>=<value1> \
 -D<key2>=<value2> \
 ...

# Use defaults
sbt

# Clear out all component names
sbt -Djapgolly.scalajs.react.component.names.all=blank

.component.names.all

Specifies the transformation to apply to all component display-names, whether automatically/implicitly specified, or explicitly specified when you create the component.

Usage:

sbt -Djapgolly.scalajs.react.component.names.all=allow|blank
Setting Outcome
allow (default) Allow all component names. Doesn't perform any transforms.
blank Clear all component names. Transforms all names into "".

.component.names.implicit

Determines how implicitly name components that haven't been created with the explicit specification of an display-name.

Usage:

sbt -Djapgolly.scalajs.react.component.names.implicit=full|short|blank
Setting Outcome
full (default) FQCN + field name (except with a trailing .Comp or .Component removed)
short The last component of the full name (above)
blank Empty string. No automatic/implicit component names.

Example:

Given the following components:

package com.example

import japgolly.scalajs.react._

object UsersEditor {
  val Component = ScalaComponent.builder[Unit].renderStatic(<.div).build
}

object Layout {
  val Header = ScalaComponent.builder[Unit].renderStatic(<.div).build
  val Footer = ScalaComponent.builder[Unit].renderStatic(<.div).build
}

Outcomes:

Setting Name Name Name
full (default) com.example.UsersEditor com.example.Layout.Header com.example.Layout.Footer
short UsersEditor Header Footer
blank

.config.class (Scala 3 only)

Instructs scalajs-react to use a custom instance of ScalaJsReactConfig that you've provided.

Usage:

Configure as follows where fqcn is the fully-qualified classname of your config object.

sbt -Djapgolly.scalajs.react.config.class=<fqcn>

And then create your object in one of the following ways:

// Recommended method
object Example1 extends ScalaJsReactConfig.Defaults {
  // override settings as desired
}

// Paranoid/full-power method
object Example2 extends ScalaJsReactConfig {

  // `transparent inline` below so that transformations are performed at compile-time
  // and only the results appear in the output JS.

  override transparent inline def automaticComponentName(name: String) =
    ??? // your impl here

  override transparent inline def modifyComponentName(name: String) =
    ??? // your impl here

  override val reusabilityOverride =
    ??? // your impl here
}

Example:

sbt -Djapgolly.scalajs.react.config.class=com.example.CustomConfig

package com.example

import japgolly.scalajs.react._

object CustomConfig extends ScalaJsReactConfig.Defaults {
  // `transparent inline` so that the transformation is performed at compile-time
  // and only the result appears in the output JS.
  override transparent inline def automaticComponentName(name: String) =
    name + " (auto)"
}

Runtime Settings: Usage

Runtime settings are designed for use in development-mode only (fastOptJS). They are omitted from production-mode output (fullOptJS).

Runtime settings must

  1. be specified in your app's main method or equivalent entrypoint
  2. be evaluated before any affected components are created

Example:

import japgolly.scalajs.react._
import org.scalajs.dom
import scala.scalajs.js.annotation._

object Main {

  @JSExportTopLevel("main")
  def main() = {

    // Apply runtime settings before any components are referenced
    Reusability.disableGloballyInDev()

    // Start app
    val container = dom.document.getElementById("root")
    val root = ReactDOMClient.createRoot(container)
    root.render(MyApp())
  }
}

Reusability.disableGloballyInDev()

Note: Runtime settings only affect development-mode (fastOptJS) and must be applied before any components are created.

This globally disables Reusability.shouldComponentUpdate so that it doesn't nothing.

ReusabilityOverlay.overrideGloballyInDev()

[ReusabilityOverlay has been deprecated in v3 with no replacement — use React's Profiler instead]

Note: Runtime settings only affect development-mode (fastOptJS) and must be applied before any components are created.

This makes calls to Reusability.shouldComponentUpdate also display a little UI overlay for you to inspect/debug component updates. You can see a live example of this in use here.

Custom ReusabilityOverride

Note: Runtime settings only affect development-mode (fastOptJS) and must be applied before any components are created.

You can modify the behaviour of Reusability.shouldComponentUpdate to apply any custom logic you like by creating your own instance of ScalaJsReactConfig.ReusabilityOverride and providing to ScalaJsReactConfig.Defaults.overrideReusabilityInDev().

Example:

import japgolly.scalajs.react._
import org.scalajs.dom
import scala.scalajs.js.annotation._

object Main {

  private object logComponents extends ScalaJsReactConfig.ReusabilityOverride {
    override def apply[P: Reusability, C <: Children, S: Reusability, B, U <: UpdateSnapshot] = b => {
      println("Detected component with Reusability.shouldComponentUpdate: " + b.name)
      b
    }
  }

  @JSExportTopLevel("main")
  def main() = {

    // Apply runtime settings before any components are referenced
    ScalaJsReactConfig.Defaults.overrideReusabilityInDev(logComponents)

    // Start app
    val container = dom.document.getElementById("root")
    val root = ReactDOMClient.createRoot(container)
    root.render(MyApp())
  }
}