Troubleshooting

Debugging your webpack config

Read the error message carefully. The error message will tell you the precise key value that is not matching what Webpack expects.
Put a debugger statement in your Webpack configuration and run bin/webpack --debug. If you have a node debugger installed, you’ll see the Chrome debugger for your webpack config. For example, install the Chrome extension NiM and set the option for the dev tools to open automatically. For more details on debugging, see the official Webpack docs on debugging

ENOENT: no such file or directory - node-sass

If you get this error ENOENT: no such file or directory - node-sass on Heroku or elsewhere during assets:precompile or bundle exec rails webpacker:compile then you would need to rebuild node-sass. It’s a bit of a weird error; basically, it can’t find the node-sass binary. An easy solution is to create a postinstall hook - npm rebuild node-sass in package.json and that will ensure node-sass is rebuilt whenever you install any new modules.

Can’t find hello_react.js in manifest.json

If you get this error Can't find hello_react.js in manifest.json when loading a view in the browser it’s because webpack is still compiling packs. Webpacker uses a manifest.json file to keep track of packs in all environments, however since this file is generated after packs are compiled by webpack. So, if you load a view in browser whilst webpack is compiling you will get this error. Therefore, make sure webpack (i.e ./bin/webpack-dev-server) is running and has completed the compilation successfully before loading a view.

throw er; // Unhandled ‘error’ event

If you get this error while trying to use Elm, try rebuilding Elm. You can do so with a postinstall hook in your package.json:

"scripts": {
  "postinstall": "npm rebuild elm"
}

webpack or webpack-dev-server not found

This could happen if webpacker:install step is skipped. Please run bundle exec rails webpacker:install to fix the issue.
If you encounter the above error on heroku after upgrading from Rails 4.x to 5.1.x, then the problem might be related to missing yarn binstub. Please run following commands to update/add binstubs:

bundle config --delete bin
./bin/rails app:update:bin # or rails app:update:bin

Running webpack on Windows

If you are running webpack on Windows, your command shell may not be able to interpret the preferred interpreter
for the scripts generated in bin/webpack and bin/webpack-dev-server. Instead you’ll want to run the scripts
manually with Ruby:

C:\path&gt;ruby bin\webpack
C:\path&gt;ruby bin\webpack-dev-server

Invalid configuration object. webpack has been initialised using a configuration object that does not match the API schema.

If you receive this error when running $ ./bin/webpack-dev-server ensure your configuration is correct; most likely the path to your “packs” folder is incorrect if you modified from the original “source_path” defined in config/webpacker.yml.

Running Elm on Continuous Integration (CI) services such as CircleCI, CodeShip, Travis CI

If your tests are timing out or erroring on CI it is likely that you are experiencing the slow Elm compilation issue described here: elm-compiler issue #1473

The issue is related to CPU count exposed by the underlying service. The basic solution involves using libsysconfcpus to change the reported CPU count.

Basic fix involves:

# install sysconfcpus on CI
git clone https://github.com/obmarg/libsysconfcpus.git $HOME/dependencies/libsysconfcpus
cd libsysconfcpus
.configure --prefix=$HOME/dependencies/sysconfcpus
make &amp;&amp; make install

# use sysconfcpus with elm-make
mv $HOME/your_rails_app/node_modules/.bin/elm-make $HOME/your_rails_app/node_modules/.bin/elm-make-old
printf "#\041/bin/bash\n\necho \"Running elm-make with sysconfcpus -n 2\"\n\n$HOME/dependencies/sysconfcpus/bin/sysconfcpus -n 2 $HOME/your_rails_app/node_modules/.bin/elm-make-old \"\$@\"" &gt; $HOME/your_rails_app/node_modules/.bin/elm-make
chmod +x $HOME/your_rails_app/node_modules/.bin/elm-make

Rake assets:precompile fails. ExecJS::RuntimeError

This error occurs because you are trying to minify by terser a pack that’s already been minified by Webpacker. To avoid this conflict and prevent appearing of ExecJS::RuntimeError error, you will need to disable uglifier from Rails config:

// production.rb
# From

Rails.application.config.assets.js_compressor = :uglifier

# To

Rails.application.config.assets.js_compressor = Uglifier.new(harmony: true)

Angular: WARNING in ./node_modules/@angular/core/esm5/core.js, Critical dependency: the request of a dependency is an expression

To silent these warnings, please update config/webpack/environment.js

// environment.js
const webpack = require('webpack')
const { resolve } = require('path')
const { environment, config } = require('@rails/webpacker')

environment.plugins.append('ContextReplacement',
  new webpack.ContextReplacementPlugin(
    /angular(\\|\/)core(\\|\/)(@angular|esm5)/,
    resolve(config.source_path)
  )
)

Modules

Classes

docs/troubleshooting