| # c8 - native V8 code-coverage | |
| [](https://github.com/bcoe/c8/actions/workflows/ci.yaml) | |
|  | |
| [](https://www.conventionalcommits.org/) | |
| Code-coverage using [Node.js' built in functionality](https://nodejs.org/dist/latest-v10.x/docs/api/cli.html#cli_node_v8_coverage_dir) | |
| that's compatible with [Istanbul's reporters](https://istanbul.js.org/docs/advanced/alternative-reporters/). | |
| Like [nyc](https://github.com/istanbuljs/nyc), c8 just magically works: | |
| ```sh | |
| npm i c8 -g | |
| c8 node foo.js | |
| ``` | |
| The above example will output coverage metrics for `foo.js`. | |
| ## CLI Options / Configuration | |
| c8 can be configured via command-line flags, a `c8` section in `package.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 from | |
| `cwd` and walking up the filesystem tree. | |
| When using `package.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. Run `c8 --help` for the full list and documentation. | |
| | Option | Description | Type | Default | | |
| | ------ | ----------- | ---- | ------- | | |
| | `-c`, `--config` | path to JSON configuration file | `string` | See above | | |
| | `-r`, `--reporter` | coverage reporter(s) to use | `Array<string>` | `['text']` | | |
| | `-o`, `--reports-dir`, `--report-dir` | directory where coverage reports will be output to | `string` | `./coverage` | | |
| | `--all` | see [section below](#checking-for-full-source-coverage-using---all) for more info | `boolean` | `false` | | |
| | `--src` | see [section below](#checking-for-full-source-coverage-using---all) for more info | `Array<string>` | `[process.cwd()]`| | |
| | `-n`, `--include` | see [section below](#checking-for-full-source-coverage-using---all) for more info | `Array<string>` | `[]` (include all files) | | |
| | `-x`, `--exclude` | see [section below](#checking-for-full-source-coverage-using---all) for more info | `Array<string>` | [list](https://github.com/istanbuljs/schema/blob/master/default-exclude.js) | | |
| | `--exclude-after-remap` | see [section below](#exclude-after-remap) for more info | `boolean` | `false` | | |
| | `-e`, `--extension` | only files matching these extensions will show coverage | `string \| Array<string>` | [list](https://github.com/istanbuljs/schema/blob/master/default-extension.js) | | |
| | `--skip-full` | do not show files with 100% statement, branch, and function coverage | `boolean` | `false` | | |
| | `--check-coverage` | check whether coverage is within thresholds provided | `boolean` | `false` | | |
| | `--per-file` | check thresholds per file | `boolean` | `false` | | |
| | `--temp-directory` | directory V8 coverage data is written to and read from | `string` | `process.env.NODE_V8_COVERAGE` | | |
| | `--clean` | should temp files be deleted before script execution | `boolean` | `true` | | |
| ## Checking for "full" source coverage using `--all` | |
| By default v8 will only give us coverage for files that were loaded by the engine. If there are source files in your | |
| project that are flexed in production but not in your tests, your coverage numbers will not reflect this. For example, | |
| if your project's `main.js` loads `a.js` and `b.js` but your unit tests only load `a.js` your total coverage | |
| could show as `100%` for `a.js` when in fact both `main.js` and `b.js` are uncovered. | |
| By supplying `--all` to c8, all files in directories specified with `--src` (defaults to `cwd`) that pass the `--include` | |
| and `--exclude` flag checks, will be loaded into the report. If any of those files remain uncovered they will be factored | |
| into the report with a default of 0% coverage. | |
| ## SourceMap Support | |
| `c8` can handle source-maps, for remapping coverage from generated code to original source files (_useful for TypeScript, JSX, etc_). | |
| ### Source map files versus inline source maps | |
| 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., running `tsc` 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. | |
| ### Exclude after remap | |
| 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. | |
| ## c8 report | |
| run `c8 report` to regenerate reports after `c8` has already been run. | |
| ## Checking coverage | |
| c8 can fail tests if coverage falls below a threshold. | |
| After running your tests with c8, simply run: | |
| ```sh | |
| c8 check-coverage --lines 95 --functions 95 --branches 95 | |
| ``` | |
| c8 also accepts a `--check-coverage` shorthand, which can be used to | |
| both run tests and check that coverage falls within the threshold provided: | |
| ```sh | |
| c8 --check-coverage --lines 100 npm test | |
| ``` | |
| The above check fails if coverage falls below 100%. | |
| To check thresholds on a per-file basis run: | |
| ```sh | |
| c8 check-coverage --lines 95 --per-file | |
| ``` | |
| If you want to check for 100% coverage across all dimensions, use `--100`: | |
| ```sh | |
| c8 --100 npm test | |
| ``` | |
| Is equivalent to | |
| ```sh | |
| c8 --check-coverage --lines 100 --functions 100 --branches 100 --statements 100 npm test | |
| ``` | |
| The `--100` flag can be set for the `check-coverage` as well: | |
| ```sh | |
| c8 check-coverage --100 | |
| ``` | |
| ## Ignoring Uncovered Lines, Functions, and Blocks | |
| Sometimes you might find yourself wanting to ignore uncovered portions of your | |
| codebase. For example, perhaps you run your tests on Linux, but | |
| there's some logic that only executes on Windows. | |
| To ignore lines, blocks, and functions, use the special comment: | |
| `/* c8 ignore next */`. | |
| ### Ignoring the next line | |
| ```js | |
| const myVariable = 99 | |
| /* c8 ignore next */ | |
| if (process.platform === 'win32') console.info('hello world') | |
| ``` | |
| ### Ignoring the next N lines | |
| ```js | |
| const myVariable = 99 | |
| /* c8 ignore next 3 */ | |
| if (process.platform === 'win32') { | |
| console.info('hello world') | |
| } | |
| ``` | |
| ### Ignoring all lines until told | |
| ```js | |
| /* c8 ignore start */ | |
| function dontMindMe() { | |
| // ... | |
| } | |
| /* c8 ignore stop */ | |
| ``` | |
| ### Ignoring a block on the current line | |
| ```js | |
| const myVariable = 99 | |
| const os = process.platform === 'darwin' ? 'OSXy' /* c8 ignore next */ : 'Windowsy' | |
| ``` | |
| ## Supported Node.js Versions | |
| c8 uses [native V8 coverage](https://github.com/nodejs/node/pull/22527), | |
| make sure you're running Node.js `>= 12`. | |
| ## Contributing to `c8` | |
| See the [contributing guide here](./CONTRIBUTING.md). | |