vertx module not found when using webpack

Question

When using webpack and libraries that want to use when.js (when), it is possible that the following error is thrown when compiling:

[2] ERROR in ./node_modules/when/lib/env.js 32:14-35
[2] Module not found: Error: Can't resolve 'vertx' in 'path-to-project/node_modules/when/lib'

The issue seems to be isolated to webpack, and is documented on when's github. Running npm install vertx or npm install @vertx/core will not resolve the issue either, since the problem lays in the import of vertx in the when library.

Answer 1

To resolve the issue:

Install @vertx/core (npm i @vertx/core)

Edit the file ./node_modules/when/lib/env.js, and change line 32 from

var vertx = vertxRequire('vertx');

to

var vertx = vertxRequire('@vertx/core');

This will reference the @vertx/core package instead of the vertx package, which does not seem to be able to be found when using webpack and npm. I haven't experienced any issues with just using vertx/core. You might also need to update your gitignore to include the changes to the library if others are also working on your project.

Answer 2

The issue can indeed be solved by adding the @vertex/core package, but instead of editing the ./node_modules/when/lib/env.js file manually as recommended by @Todd Rylaarsdam, I'd use the NormalModuleReplacementPlugin in your Webpack config to replace the old vertx package, like so:

new webpack.NormalModuleReplacementPlugin(
  /^vertx/,
  '@vertx/core',
)

This way you don't have to make any manual changes to the files of a package you're using.

See https://webpack.js.org/plugins/normal-module-replacement-plugin/ for more info about this plugin.