source-map-loader/README.md

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# source-map-loader

Extracts source maps from existing source files (from their <code>sourceMappingURL</code>).

## Getting Started

To begin, you'll need to install `source-map-loader`:

```bash
npm i -D source-map-loader
```

Then add the plugin to your `webpack` config. For example:

**file.js**

```js
import css from "file.css";
```

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        enforce: "pre",
        use: ["source-map-loader"],
      },
    ],
  },
};
```

The `source-map-loader` extracts existing source maps from all JavaScript entries.
This includes both inline source maps as well as those linked via URL.
All source map data is passed to webpack for processing as per a chosen [source map style](https://webpack.js.org/configuration/devtool/) specified by the `devtool` option in [webpack.config.js](https://webpack.js.org/configuration/).
This loader is especially useful when using 3rd-party libraries having their own source maps.
If not extracted and processed into the source map of the webpack bundle, browsers may misinterpret source map data. `source-map-loader` allows webpack to maintain source map data continuity across libraries so ease of debugging is preserved.
The `source-map-loader` will extract from any JavaScript file, including those in the `node_modules` directory.
Be mindful in setting [include](https://webpack.js.org/configuration/module/#rule-include) and [exclude](https://webpack.js.org/configuration/module/#rule-exclude) rule conditions to maximize bundling performance.

And run `webpack` via your preferred method.

## Options

|                          Name                           |     Type     |   Default   | Description                                    |
| :-----------------------------------------------------: | :----------: | :---------: | :--------------------------------------------- |
| **[`filterSourceMappingUrl`](#filtersourcemappingurl)** | `{Function}` | `undefined` | Allows to control `SourceMappingURL` behaviour |

### filterSourceMappingUrl

Type: `Function`
Default: `undefined`

Allows you to specify the behavior of the loader for `SourceMappingURL` comment.

The function must return one of the values:

- `true` or `'consume'` - consume the source map and remove `SourceMappingURL` comment (default behavior)
- `false` or `'remove'` - do not consume the source map and remove `SourceMappingURL` comment
- `skip` - do not consume the source map and do not remove `SourceMappingURL` comment

Example configuration:

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        enforce: "pre",
        use: [
          {
            loader: "source-map-loader",
            options: {
              filterSourceMappingUrl: (url, resourcePath) => {
                if (/broker-source-map-url\.js$/i.test(url)) {
                  return false;
                }

                if (/keep-source-mapping-url\.js$/i.test(resourcePath)) {
                  return "skip";
                }

                return true;
              },
            },
          },
        ],
      },
    ],
  },
};
```

## Examples

### Ignoring Warnings

To ignore warnings, you can use the following configuration:

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        enforce: "pre",
        use: ["source-map-loader"],
      },
    ],
  },
  ignoreWarnings: [/Failed to parse source map/],
};
```

More information about the `ignoreWarnings` option can be found [here](https://webpack.js.org/configuration/other-options/#ignorewarnings)

## Contributing

Please take a moment to read our contributing guidelines if you haven't yet done so.

[CONTRIBUTING](./.github/CONTRIBUTING.md)

## License

[MIT](./LICENSE)

[npm]: https://img.shields.io/npm/v/source-map-loader.svg
[npm-url]: https://npmjs.com/package/source-map-loader
[node]: https://img.shields.io/node/v/source-map-loader.svg
[node-url]: https://nodejs.org
[deps]: https://david-dm.org/webpack-contrib/source-map-loader.svg
[deps-url]: https://david-dm.org/webpack-contrib/source-map-loader
[tests]: https://github.com/webpack-contrib/source-map-loader/workflows/source-map-loader/badge.svg
[tests-url]: https://github.com/webpack-contrib/source-map-loader/actions
[cover]: https://codecov.io/gh/webpack-contrib/source-map-loader/branch/master/graph/badge.svg
[cover-url]: https://codecov.io/gh/webpack-contrib/source-map-loader
[chat]: https://badges.gitter.im/webpack/webpack.svg
[chat-url]: https://gitter.im/webpack/webpack
[size]: https://packagephobia.now.sh/badge?p=source-map-loader
[size-url]: https://packagephobia.now.sh/result?p=source-map-loader