Scala.js runtime error: require is not a function

Problem

In Scala.js, Coursier’s NPM dependencies are loaded through js.Dynamic.global.require("..."). This is problematic for two reasons:

• Incompatibility with ES modules.

  Scala.js projects depending on Coursier should have the choice between generating ES module imports or CommonJS requires, but the current implementation of Coursier contains hard-coded calls to require. This means that Scala.js projects targeting ES modules will also generate require calls, which won’t work in the browser (unless the bundle is passed through a bundler like Webpack).

• global.require may be undefined depending on how the JS code is loaded.

  For instance, running console.log(global.require) prints undefined in a JS file (loaded using node test.js) but prints the require function in a Node.js REPL. See this StackOverflow question.

These two reasons both lead to the same runtime error: TypeError: $g.require is not a function.

Solution

There are two possible solutions for this:

1. Use @JSImport over js.Dynamic.global.require.
2. Update to Scala.js 1.x and use @JSGlobal to access require instead of global.require.

I think solution 1 is probably preferable to solution 2, as Scala.js projects can then target the module system they need. While I think Coursier should eventually move to Scala.js 1.x, solution 2 requires getting all of Coursier’s dependencies to switch to 1.x, which may take time.

Workaround until the solution is implemented

If anyone else needs to work around the issue for now, the hack I’ve found is to use Webpack to bundle my Scala.js output with a JS file containing eval("global.require = require"). Note that you should then very carefully determine if the Coursier dependencies (xhr2, cheerio, xmldom and sax) should be bundled too (for the Web) or just be available in node_modules (for Node.js).

[MaximeKjaer]

I updated my project to Scala.js 1.1.0 and Coursier v2.0.0-RC6-21, and can confirm that #1715 fixes the problem. I’ll be closing this issue – thank you!

[alexarchambault]

Otherwise, since scalajs-react will very soon be releasing for 1.0, it may also be acceptable to just let this issue be the documentation for the workaround in the meantime, and solve the issue by upgrading to 1.0.

Let’s do this for now then. I don’t really know how many people depend on / use coursier via its Scala.JS artifacts, they’ll find this issue if needed, yes.