Troubleshooting

Common issues and solutions when working with CEM.

Manifest is empty

Make sure your glob pattern matches your files:

cem generate --verbose

Check the .config/cem.yaml generate.files glob pattern matches your source files.

Component not showing in dev server

1. Regenerate manifest: cem generate
2. Check file patterns: Verify generate.files glob in .config/cem.yaml
3. Verify package.json: Ensure customElements field exists
4. Verify manifest content: cem list
5. Check demos: Ensure demo files exist and are discoverable
6. Restart the server: cem serve

Demos not discovered

Check demo file location matches discovery patterns:

• Files in demo/ or demos/ directories
• Files named *.demo.html
• Or configured in .config/cem.yaml

See Working with Demos for details on demo discovery configuration.

TypeScript errors

Ensure you have a tsconfig.json:

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "ES2022",
    "moduleResolution": "bundler",
    "experimentalDecorators": true
  }
}

LSP features not working

1. Check manifest exists: ls custom-elements.json
2. Verify manifest content: cem list
3. Verify LSP is running: Check editor’s LSP status
4. Regenerate if stale: cem generate
5. Check LSP logs in your editor
6. Restart editor: Reload window

See Using LSP Features for more details.

Dev server won’t start

Check for port conflicts:

# Try a different port
cem serve --port 3000

Check for syntax errors:

# Validate your manifest
cem validate

Import maps not working

1. Check package.json: Ensure dependencies are listed
2. Restart server: cem serve picks up package.json on startup
3. Clear browser cache: Hard reload (Ctrl+Shift+R / Cmd+Shift+R)

See Import Maps for configuration details.

Changes not refreshing

1. Check live reload is enabled (default)
2. Look for errors in browser console
3. Verify source maps for TypeScript
4. Clear browser cache if needed

Get Help

• Documentation - Browse all docs
• GitHub Issues - Report bugs or request features
• Examples - See working examples