Add the following to your project definition files:

<root>/project/plugins.sbt

addSbtPlugin("com.github.lionelfleury" % "sbt-scalajs-callgraph" % "0.1.2")

<root>/build.sbt

enablePlugins(CallGraphPlugin)

Run the new added SBT command:

sbt callgraph

It's also possible to generate the callgraph for your tests simply use:

sbt test:callgraph

You get callgraph.html (or callgraph-test.html) in your target directory. Open the html file and start exploring your Scala.js project's call graph...

If you want the development stage version, change to the following:

resolvers += Resolver.sonatypeRepo("snapshots")
addSbtPlugin("com.github.lionelfleury" % "sbt-scalajs-callgraph" % "0.1.3-SNAPSHOT")

If you're interested in contributing to this project, simply fork the repo and open a new pull request when you're ready. If you're working on the ScalaJS part, you might want to use the command:

sbt callgraph-dev

to test your modifications. This command generates a callgraph-dev.html using the local version of the javascript files.