Question 1

How to run Phantomas in Docker for isolated testing?

Accepted Answer

Phantomas provides official Docker images on Docker Hub and GitHub Container Registry. Pull the image and use commands like `docker run macbre/phantomas http://example.com` to execute tests without local dependencies, ideal for CI environments.

Question 2

Phantomas vs Lighthouse: which is better for performance analysis?

Accepted Answer

Use Phantomas for deep, customizable frontend metrics like CSS complexity and custom JS tracking, with a modular approach. Lighthouse is better for holistic audits including SEO and accessibility, but Phantomas excels in granular performance data and extensibility.

Question 3

How to emit custom metrics from my webpage using Phantomas?

Accepted Answer

Inject helper functions from window.__phantomas in your page's JavaScript. For example, call `window.__phantomas.emitMetric('myMetric', value)` during page load to send custom data back to Phantomas for analysis in the results.

Question 4

Can Phantomas handle authenticated pages or login flows?

Accepted Answer

Yes, but it requires additional configuration. Use Puppeteer options passed via the API to set cookies, headers, or run custom scripts before capturing metrics, though this adds complexity compared to simpler tools.

Question 5

What metrics does Phantomas provide for JavaScript performance?

Accepted Answer

It includes metrics like jQuery event bindings, document.write calls, and DOM query counts. These help identify inefficient JS patterns that impact page load and interactivity, complementing timing-based metrics.

Question 6

How to integrate Phantomas into a CI/CD pipeline like GitHub Actions?

Accepted Answer

Install it as an npm dependency, run it in a script that outputs JSON, and parse the results for performance thresholds. Example workflows are community-driven, as the README mentions integration with tools but lacks detailed CI examples.

Question 7

Is Phantomas good for monitoring performance regressions over time?

Accepted Answer

Yes, its JSON output and modular metrics make it suitable for building performance budgets. However, you'll need to set up external storage and dashboards, as it doesn't include built-in historical tracking or alerting features.

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