@stryker-mutator/javascript-mutator/README.md

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# Stryker JavaScript mutator

A mutator that supports JavaScript for [Stryker](https://stryker-mutator.io), the JavaScript Mutation testing framework. This plugin does not transpile any code. The code that the @stryker-mutator/javascript-mutator gets should be executable in your environment (i.e. the @stryker-mutator/javascript-mutator does not add support for Babel projects). 

## Quickstart

First, install Stryker itself (you can follow the [quickstart on the website](https://stryker-mutator.io/quickstart.html))

Next, install this package:

```bash
npm install --save-dev @stryker-mutator/javascript-mutator
```

Now open up your stryker.conf.js file and add the following components:

```javascript
mutator: 'javascript',
// OR
mutator: {
    name: 'javascript',
    plugins: ['classProperties', 'optionalChaining'],
    excludedMutations: ['BooleanSubstitution', 'StringLiteral']
}
```

Now give it a go:

```bash
$ stryker run
```

## Configuration

### `mutator.name` [`string`]

The name of the mutator, use `'javascript'` to enable this mutator.

### `mutator.plugins` [`(string | ParserPluginWithOptions)[]`]

Default: `['asyncGenerators', 'bigInt', 'classProperties', 'dynamicImport', 'flow', 'jsx', 'objectRestSpread', ['decorators', { decoratorsBeforeExport: true }]`

Configure custom [Babel Syntax plugins](https://babeljs.io/docs/en/babel-parser#plugins). Syntax plugins allow you to parse different pieces of syntax. 
By default a number of plugins are configured. We might add more in the future. For example: you can configure your own Syntax plugins here to allow for [stage 1](https://github.com/tc39/proposals/blob/master/stage-1-proposals.md) features. 

### `mutator.excludedMutations` [`string[]`]

See [Stryker core's readme](https://github.com/stryker-mutator/stryker/tree/master/packages/core#mutator)

## Mutators

The `JavaScript Mutator` is a plugin to mutate JavaScript code. This is done using Babel without any plugins.

See [test code](https://github.com/stryker-mutator/stryker/tree/master/packages/javascript-mutator/test/unit/mutators) to know which mutations are supported.