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Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →To run Loki screenshot tests in Docker, start your Storybook server, create a baseline with yarn loki update, then compare later captures with yarn loki test. Loki does not launch Storybook for you. Review screenshots and diffs before approving any changed reference.
What you need before running Loki in Docker
- A Storybook project and Loki installed as a development dependency.
- Docker available to the account that runs Loki.
- A Node.js version compatible with your installed Loki and Storybook versions.
Loki’s getting-started documentation, last updated 2024-08-27, lists Node 16+ for its setup. Treat that as historical guidance, not a verified compatibility promise for current releases; check the documentation for the Loki version installed in your project. The same caution applies to Docker image defaults and CLI options. Loki getting started
Install and initialize Loki
- From the project directory, install Loki:
yarn add loki --dev. - Initialize its configuration:
yarn loki init. - Check the generated configuration and confirm that the installed Loki version supports the options you intend to use.
Start Storybook before capture
Start the Storybook server in a separate terminal before running Loki. The project documentation states: “For loki to be able to access your stories you must start the storybook server.” A typical command is yarn storybook; use your project’s actual script if it differs. Loki getting started
If Storybook listens on a non-default port or host, pass the matching values using the CLI’s --port and --host options. Confirm the syntax supported by the Loki and package-manager versions in use. For example, the Loki CLI documentation shows forwarding a port option with yarn loki test -- --port 9009; package managers can differ in how they forward arguments. Loki CLI
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Create baselines and run comparisons
- With Storybook running, generate the initial reference screenshots:
yarn loki update. - Commit the approved references with the project. Loki’s getting-started guide says Git LFS is optional.
- For later visual regression runs, execute
yarn loki test. - Inspect both captured screenshots and the generated differences. Only accept a change after confirming it is intentional.
- When a UI change is expected, update the reference using
yarn loki approve, or use the command Loki suggests to approve only failing stories when that is the intended scope.
The CLI documentation lists these default output directories: references in ./.loki/reference, fresh captures in ./.loki/current, and differences in ./.loki/difference. It also lists pixelmatch, looks-same, and gm as diff engines. These documented defaults may vary by release, so verify them against the installed CLI before depending on a path or engine. Loki CLI
Configure Loki’s Chrome Docker target
Loki documents Chrome in Docker as a supported capture target. Its CLI options let you adjust how the Chrome container runs and how it reaches your Storybook server. The CLI reference was last updated 2024-08-27; check your installed version before copying version-specific values. Loki CLI
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| Option | What it controls | When to consider changing it |
|---|---|---|
--chromeDockerImage |
Selects the Chrome container image. | When the documented or configured image does not suit the installed Loki version or your environment. |
--dockerNet |
Passes a Docker network mode, such as host or bridge. |
When Chrome in the container cannot reach Storybook using the current network setup. There is no universally correct mode for every CI environment. |
--chromeDockerUseCopy |
Copies local stories instead of using a volume mount. | When mounting local files is unavailable or unreliable in the environment. |
--dockerWithSudo |
Invokes Docker with sudo. |
When the environment requires elevated permissions for Docker commands. |
The CLI page lists yukinying/chrome-headless-browser-stable:118.0.5993.117 as a default Chrome Docker image. That is a historical documented value, not a current recommendation. Confirm the right image for your installed Loki version before setting or relying on it. Loki CLI
Pass Docker settings through the package manager
When using Yarn or npm, Loki’s CLI documentation says to put -- before Loki arguments so the package manager forwards them. For example: yarn loki test -- --port 9009. Apply the same forwarding pattern for Docker options if supported by your installed CLI, and check your package manager’s conventions if the arguments are not received as expected. Loki CLI
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Make screenshots stable and repeatable
Control external requests and data
By default, a failed network request from a story fails the test. Avoid depending on live services or changing remote data where possible; provide controlled responses so a temporary outage or content change does not look like a visual regression. Loki configuration
Handle animation and asynchronous rendering
Animation timing can change the captured frame between runs. Loki’s flaky-test guidance documents disabling animations with the chromeEnableAnimations option. For stories that finish rendering asynchronously, use the documented callback pattern to signal completion rather than capturing before the final UI is ready. Loki flaky tests
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Troubleshoot common Docker test failures
| Symptom | Likely cause | What to check |
|---|---|---|
| Loki cannot load stories | Storybook is not running, or Loki is pointed at the wrong host or port. | Start Storybook first, confirm it is reachable, then align Loki’s host and port settings with the server. |
| Chrome in Docker cannot connect to Storybook | The selected Docker network cannot reach the Storybook server. | Check the configured host, port, and --dockerNet mode. Test an appropriate network mode for your local or CI environment; the docs do not prescribe one mode for every setup. |
| Files or stories are unavailable inside the capture environment | A volume mount is not working in the environment. | Check mount access and consider --chromeDockerUseCopy to copy local stories instead. |
| Docker exits with a permissions error | The runner cannot invoke Docker with its current permissions. | Check the runner’s Docker access; use --dockerWithSudo only if that environment requires sudo. |
| Tests fail after a network request fails | The story depends on an unavailable or unstable request. | Stub or otherwise control the request and its data for deterministic rendering. |
| Diffs vary across runs without an intentional UI change | Animation timing or unfinished asynchronous rendering may be changing the frame. | Disable animations where appropriate and signal completion for asynchronous stories. |
| Every story shows a difference | The reference may be stale, or capture conditions may have changed. | Inspect images in ./.loki/reference, ./.loki/current, and ./.loki/difference; verify the environment before approving references. |
Or skip the browser setup
If you need a clean screenshot without configuring Loki and Docker, ScreenshotNeo offers a one-request screenshot API. The following cURL command captures a page as WebP; see the ScreenshotNeo API documentation for parameters and response details.
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webp
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Frequently Asked Questions
Does Loki start Storybook automatically?
No. Start the Storybook server before running Loki.
Which command creates the first reference screenshots?
Run yarn loki update while Storybook is available.
Can I use Docker with a different Chrome image?
The CLI documents --chromeDockerImage; check the requirements for your installed Loki version before choosing an image.
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