c8

What is c8?

The c8 npm package is a code coverage tool for JavaScript that works with the native V8 coverage functionality built into Node.js. It collects and reports on the test coverage of your code, helping you understand which parts of your codebase are covered by tests and which are not.

What are c8's main functionalities?

Code Coverage Reporting

This command runs your Node.js script with coverage tracking, and upon completion, it outputs a coverage report. The report shows the percentage of code executed by your tests, helping you identify untested parts of your codebase.

npx c8 node script.js

Integration with Testing Frameworks

You can use c8 in conjunction with testing frameworks like Mocha. This command will run Mocha tests with coverage tracking, and then generate a coverage report.

npx c8 mocha

Custom Report Formats

c8 allows you to specify one or more reporters that determine the format of the coverage report. In this example, it generates both 'lcov' and 'text' format reports.

npx c8 --reporter=lcov --reporter=text node script.js

Check Coverage Thresholds

This feature allows you to enforce coverage thresholds. If the coverage falls below the specified percentages for lines, functions, or branches, c8 will exit with a non-zero status, which is useful for CI/CD pipelines.

npx c8 --check-coverage --lines 95 --functions 95 --branches 95 node script.js

Other packages similar to c8

nyc

Previously known as Istanbul, nyc is another popular code coverage tool for JavaScript. It works with a wide range of testing frameworks and can instrument code for coverage reporting. Compared to c8, nyc has been around longer and has more configuration options, but c8 is built to leverage the native V8 coverage and might be faster and more accurate for Node.js applications.

jest

Jest is a testing framework that includes built-in code coverage reporting. While Jest is primarily a testing framework, its coverage tool is often compared to standalone tools like c8. Jest's coverage is implemented using Istanbul under the hood. Compared to c8, Jest provides an all-in-one solution for testing and coverage but may not be as lightweight if you only need coverage reporting.

coveralls

Coveralls is a web service that helps you track your code coverage over time, ensure that all your new code is fully covered, and integrate with your CI environment. While not a coverage tool itself, it works with tools like c8 or nyc to provide visibility into code coverage statistics. Compared to c8, Coveralls adds a layer of historical tracking and visualization to coverage data.

README

c8 - native V8 code-coverage

Code-coverage using V8's Inspector that's compatible with Istanbul's reporters.

Like nyc, c8 just magically works:

npm i c8 -g
c8 node foo.js

The above example will collect coverage for foo.js using V8's inspector.

c8 report

run c8 report to regenerate reports after c8 has already been run.

Disclaimer

c8 uses bleeding edge Node.js features, make sure you're running Node.js >= 10.10.0.