istanbul

Tracks statement, line, function, and branch coverage, providing detailed insights into test effectiveness across various environments, as emphasized in the features.

Uses module loader hooks to instrument code on the fly without requiring test runner cooperation, making it easy to add coverage to node unit tests transparently.

Generates reports in HTML, LCOV, Cobertura, and other formats, catering to different needs such as CI pipelines or local analysis, as highlighted in the command-line tools.

Works for server-side (node.js) unit tests, browser tests via instrumentation, and as middleware for server-side coverage, supporting diverse testing scenarios.