"Failed to execute postMessage..."?

Fixtures Not Detected?

  • Run cosmos with the --expose-imports flag. This should generate cosmos.imports.js. Check that file to see if your fixtures are being picked up by Cosmos.
  • Check your directory structure. If you are using a Cosmos config file, Cosmos will use the directory of the config file as the root of your project. If your Cosmos config file is nested in a directory that isn't an ancestor of your fixture files Cosmos won't find your fixtures. To solve this add a rootDir entry to your Cosmos config pointing to your root directory.



Most React Cosmos Webpack issues are related to missing build dependencies. Please see Webpack config.

localhost:5000/renderer.html 404s?

  • Check for build errors in your terminal.
  • Make sure you have html-webpack-plugin installed, as well as any other build dependency.

Renderer Not Responding?

  • Try renaming filename in HtmlWebpackPlugin options to index.html, or alternatively remove the HtmlWebpackPlugin plugin from your Webpack config and Cosmos will automatically it with the proper options. For more details see this issue (opens in a new tab).

localhost:3001/__get-internal-source... 404s?

main.js Cached in Static Exports?