Webpacker can't find application in ... manifest.json (at runtime)

Steps to reproduce

Follow the Get started with Webpacker instruction exactly, except with an existing app.

Expected behavior

Render my component.

Actual behavior

Upon hitting the route that serves the view with the react component, get this:

Webpacker can't find application in <my app path>/public/packs/manifest.json. Possible causes:
1. You want to set webpacker.yml value of compile to true for your environment
   unless you are using the `webpack -w` or the webpack-dev-server.
2. webpack has not yet re-run to reflect updates.
3. You have misconfigured Webpacker's config/webpacker.yml file.
4. Your webpack configuration is not creating a manifest.
Your manifest contains:
{
}

The message is correct, there is no public/packs/manifest.json file. That was not in the instructions, so I assume it is supposed to be created, I guess by the webpack dev server.

I updated yarn to the latest version: 1.16.0.

System configuration

Webpacker version: 4.0.7 React-Rails version: 2.5.0 Rails version: 5.2.3 Ruby version: 2.6.3

[BookOfGreg]

Node modules get corrupt all the time. Javascript does this often, I tend to see this myself randomly once a month. Especially prevalent on Windows, still happens but less often on Ubuntu. I tend to trash all current assets and modules and do a clean rebuild.

rm -rf node_modules
rails assets:clobber
yarn
rails assets:precompile

If that doesn’t so it, check you can install them gem onto a rails new foo --webpack application to confirm it’s not something with your machine. If that works and it’s still not working then it’s some config in your existing app.

[Sumeet-Raina]

Ran into this issue today while setting up a new Rails app.

Webpacker can't find application in <my app path>/public/packs/manifest.json. Possible causes:
1. You want to set webpacker.yml value of compile to true for your environment
   unless you are using the `webpack -w` or the webpack-dev-server.
2. webpack has not yet re-run to reflect updates.
3. You have misconfigured Webpacker's config/webpacker.yml file.
4. Your webpack configuration is not creating a manifest.
Your manifest contains:
{
}

while running $ bundle exec rails webpacker:install

I spotted following error in the console

error portfolio@0.1.0: The engine "node" is incompatible with this module. Expected version ">= 10.13.0". Got "10.0.0"
error Found incompatible module.

After a lot of trial and error I learnt that you can just resolve this issue in 3 steps:

$ node -v
$ nvm install 10.13.0
$ bundle exec rails webpacker:install