npm start doesn’t detect changes
When you save a file while
npm start is running, the browser should refresh with the updated code.
If this doesn’t happen, try one of the following workarounds:
- If your project is in a Dropbox folder, try moving it out.
- If the watcher doesn’t see a file called
index.jsand you’re referencing it by the folder name, you need to restart the watcher due to a Webpack bug.
- Some editors like Vim and IntelliJ have a “safe write” feature that currently breaks the watcher. You will need to disable it. Follow the instructions in “Adjusting Your Text Editor”.
- If your project path contains parentheses, try moving the project to a path without them. This is caused by a Webpack watcher bug.
- On Linux and macOS, you might need to tweak system settings to allow more watchers.
- If the project runs inside a virtual machine such as (a Vagrant provisioned) VirtualBox, create an
.envfile in your project directory if it doesn’t exist, and add
CHOKIDAR_USEPOLLING=trueto it. This ensures that the next time you run
npm start, the watcher uses the polling mode, as necessary inside a VM.
If none of these solutions help please leave a comment in this thread.
npm test hangs or crashes on macOS Sierra
We recommend deleting
node_modules in your project and running
npm install (or
yarn if you use it) first. If it doesn't help, you can try one of the numerous workarounds mentioned in these issues:
It is reported that installing Watchman 4.7.0 or newer fixes the issue. If you use Homebrew, you can run these commands to update it:
watchman shutdown-server brew update brew reinstall watchman
You can find other installation methods on the Watchman documentation page.
If this still doesn’t help, try running
launchctl unload -F ~/Library/LaunchAgents/com.github.facebook.watchman.plist.
There are also reports that uninstalling Watchman fixes the issue. So if nothing else helps, remove it from your system and try again.
npm run build exits too early
It is reported that
npm run build can fail on machines with limited memory and no swap space, which is common in cloud environments. Even with small projects this command can increase RAM usage in your system by hundreds of megabytes, so if you have less than 1 GB of available memory your build is likely to fail with the following message:
The build failed because the process exited too early. This probably means the system ran out of memory or someone called
kill -9on the process.
If you are completely sure that you didn't terminate the process, consider adding some swap space to the machine you’re building on, or build the project locally.
npm run build fails on Heroku
This may be a problem with case sensitive filenames. Please refer to this section.
Moment.js locales are missing
If you use a Moment.js, you might notice that only the English locale is available by default. This is because the locale files are large, and you probably only need a subset of all the locales provided by Moment.js.
To add a specific Moment.js locale to your bundle, you need to import it explicitly.
import moment from 'moment'; import 'moment/locale/fr';
If you are importing multiple locales this way, you can later switch between them by calling
moment.locale() with the locale name:
import moment from 'moment'; import 'moment/locale/fr'; import 'moment/locale/es'; // ... moment.locale('fr');
This will only work for locales that have been explicitly imported before.
npm run build fails to minify
email@example.com, this problem was caused by third party
firstname.lastname@example.org and higher.
If you're seeing this error, you're likely using an old version of
react-scripts. You can either fix it by avoiding a dependency that uses modern syntax, or by upgrading to
react-scripts@>=2.0.0 and following the migration instructions in the changelog.