Code-coverage usingNode.js' built in functionalitythat's compatible withIstanbul's reporters.

Likenyc, c8 just magically works:

npm i c8 -gc8 node foo.js

The above example will output coverage metrics forfoo.js.

c8 can be configured via command-line flags, ac8 section inpackage.json, or a JSON configuration file on disk.

A configuration file can be specified by passing its path on the command line with--config or-c. If no config option is provided, c8 searches for files named.c8rc,.c8rc.json,.nycrc, or.nycrc.json, starting fromcwd and walking up the filesystem tree.

When usingpackage.json configuration or a dedicated configuration file, omit the-- prefix from the long-form of the desired command-line option.

Here is a list of common options. Runc8 --help for the full list and documentation.

By default v8 will only give us coverage for files that were loaded by the engine. If there are source files in yourproject that are flexed in production but not in your tests, your coverage numbers will not reflect this. For example,if your project'smain.js loadsa.js andb.js but your unit tests only loada.js your total coveragecould show as100% fora.js when in fact bothmain.js andb.js are uncovered.

By supplying--all to c8, all files in directories specified with--src (defaults tocwd) that pass the--includeand--exclude flag checks, will be loaded into the report. If any of those files remain uncovered they will be factoredinto the report with a default of 0% coverage.

c8 can handle source-maps, for remapping coverage from generated code to original source files (useful for TypeScript, JSX, etc).

Just-in-time instrumented codebases will often insert source maps inline with the.js code they generate at runtime (e.g,@babel/register can be configured to insert a source map footer).

Pre-instrumented codebases, e.g., runningtsc to generate.js in a build folder, may generate either inline source maps, or a separate.map file stored on disk.

c8 can handle loading both types of source maps.

Depending on the size and configuration of your project, it may be preferable to apply exclusion logic either before or after source-maps are used to remap compiled to original source files.

--exclude-after-remap is used to control this behaviour.

runc8 report to regenerate reports afterc8 has already been run.

c8 can fail tests if coverage falls below a threshold.After running your tests with c8, simply run:

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

c8 also accepts a--check-coverage shorthand, which can be used toboth run tests and check that coverage falls within the threshold provided:

c8 --check-coverage --lines 100 npmtest

The above check fails if coverage falls below 100%.

To check thresholds on a per-file basis run:

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

If you want to check for 100% coverage across all dimensions, use--100:

c8 --100 npmtest

Is equivalent to

c8 --check-coverage --lines 100 --functions 100 --branches 100 --statements 100  npmtest

The--100 flag can be set for thecheck-coverage as well:

c8 check-coverage --100

Monocart is an alternate library for outputtingv8 code coverage data as Istanbul reports.

Monocart also provides reporters based directly on v8's byte-offset-based output. Such as,console-details andv8. This removes a complex transformation step and may be less bug prone for some environments.

Example usage:

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

NOTE: Monocart requires additionalmonocart-coverage-reports to be installed:

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

Sometimes you might find yourself wanting to ignore uncovered portions of yourcodebase. For example, perhaps you run your tests on Linux, butthere's some logic that only executes on Windows.

To ignore lines, blocks, and functions, use the special comment:

/* c8 ignore next */.

constmyVariable=99/* c8 ignore next */if(process.platform==='win32')console.info('hello world')

constmyVariable=99/* c8 ignore next 3 */if(process.platform==='win32'){console.info('hello world')}

/* c8 ignore start */functiondontMindMe(){// ...}/* c8 ignore stop */

constmyVariable=99constos=process.platform==='darwin' ?'OSXy'/* c8 ignore next */ :'Windowsy'

c8 usesnative V8 coverage,make sure you're running Node.js>= 12.

See thecontributing guide here.