c8

By default, V8 only provides coverage for files loaded by the engine during execution. If some files in your project are not loaded during tests, they won't appear in the report.

Use the --all flag to include all files in the directories specified by --src (defaults to cwd) that pass the --include and --exclude filters. Uncovered files will be included in the report with 0% coverage.

c8 can be configured using command-line flags, a c8 section in your package.json, or a JSON configuration file.

To specify a custom configuration file, use the --config or -c flag. If no config is provided, c8 searches for .c8rc, .c8rc.json, .nycrc, or .nycrc.json files by walking up the filesystem from the current working directory.

Note: When using package.json or a config file, omit the -- prefix from long-form command-line options.

c8 can fail your test suite if coverage falls below specified thresholds for lines, functions, branches, or statements.

Option 1: Separate check command Run tests first, then run check-coverage:

c8 check-coverage --lines 95 --functions 95 --branches 95

Option 2: Combined run and check Use the --check-coverage flag to run tests and check thresholds in one step:

c8 --check-coverage --lines 100 npm test

Option 3: Per-file threshold checking To ensure every individual file meets a threshold:

c8 check-coverage --lines 95 --per-file

Option 4: The --100 shorthand To require 100% coverage across all dimensions (lines, functions, branches, and statements):

c8 --100 npm test
# OR
c8 check-coverage --100

You can use special comments to prevent c8 from reporting uncovered lines, blocks, or functions. This is useful for platform-specific logic (e.g., code that only runs on Windows).

Ignore the next line

/* c8 ignore next */
if (process.platform === 'win32') console.info('hello world')

Ignore the next N lines

/* c8 ignore next 3 */
if (process.platform === 'win32') {
  console.info('hello world')
}

Ignore a block

/* c8 ignore start */
function dontMindMe() {
  // ...
}
/* c8 ignore stop */

Ignore a block on the current line

const os = process.platform === 'darwin' ? 'OSXy' /* c8 ignore next */ : 'Windowsy'

Monocart is an alternative library for outputting V8 coverage data as Istanbul reports. It also provides reporters based directly on V8's byte-offset-based output (like console-details and v8), which can be more robust in some environments.

Requirement: You must install monocart-coverage-reports@2 as a dev dependency.

Example usage:

c8 --experimental-monocart --reporter=v8 --reporter=console-details node foo.js

npm i monocart-coverage-reports@2 --save-dev

c8 provides native V8 code coverage compatible with Istanbul's reporters. You can install it globally and run it directly before your Node.js command to generate coverage metrics for the executed files.

npm i c8 -g
c8 node foo.js

By default, coverage tools only report on files that were actually executed. To include files that were never touched (showing 0% coverage), set all: true in the Report options.

When all is enabled, you must also provide the src option (a string or array of directory paths) so c8 knows which files to scan for existence. c8 will then create 'empty' coverage reports for those files and merge them into the final result.

If you have already run c8 and want to regenerate the coverage reports (e.g., after changing reporter settings), use the report command.

c8 report

The check-coverage command evaluates whether the coverage data in c8's output directory meets specified minimum thresholds for lines, functions, branches, and statements.

If any threshold is not met, the command sets the process exit code to 1. It can check coverage globally across all files or individually for each file.

Usage

To check if coverage meets a 95% threshold for lines, use:

c8 check-coverage --lines 95

To enforce 100% coverage across all metrics, you can use the --100 flag (which sets lines, functions, branches, and statements to 100%):

c8 check-coverage --100