source: trip-planner-front/node_modules/terser-webpack-plugin/README.md@ 188ee53

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# terser-webpack-plugin

This plugin uses [terser](https://github.com/terser-js/terser) to minify your JavaScript.

## Getting Started

If you are using webpack v5 or above you do not need to install this plugin. Webpack v5 comes with the latest `terser-webpack-plugin` out of the box. Using Webpack v4, you have to install `terser-webpack-plugin` v4.

To begin, you'll need to install `terser-webpack-plugin`:

```console
$ npm install terser-webpack-plugin --save-dev
```

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

**webpack.config.js**

```js
const TerserPlugin = require("terser-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [new TerserPlugin()],
  },
};
```

And run `webpack` via your preferred method.

## Note about source maps

**Works only with `source-map`, `inline-source-map`, `hidden-source-map` and `nosources-source-map` values for the [`devtool`](https://webpack.js.org/configuration/devtool/) option.**

Why?

- `eval` wraps modules in `eval("string")` and the minimizer does not handle strings.
- `cheap` has not column information and minimizer generate only a single line, which leave only a single mapping.

Using supported `devtool` values enable source map generation.

## Options

### `test`

Type: `String|RegExp|Array<String|RegExp>`
Default: `/\.m?js(\?.*)?$/i`

Test to match files against.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        test: /\.js(\?.*)?$/i,
      }),
    ],
  },
};
```

### `include`

Type: `String|RegExp|Array<String|RegExp>`
Default: `undefined`

Files to include.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        include: /\/includes/,
      }),
    ],
  },
};
```

### `exclude`

Type: `String|RegExp|Array<String|RegExp>`
Default: `undefined`

Files to exclude.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        exclude: /\/excludes/,
      }),
    ],
  },
};
```

### `parallel`

Type: `Boolean|Number`
Default: `true`

Use multi-process parallel running to improve the build speed.
Default number of concurrent runs: `os.cpus().length - 1`.

> ℹ️ Parallelization can speedup your build significantly and is therefore **highly recommended**.

> ⚠️ If you use **Circle CI** or any other environment that doesn't provide real available count of CPUs then you need to setup explicitly number of CPUs to avoid `Error: Call retries were exceeded` (see [#143](https://github.com/webpack-contrib/terser-webpack-plugin/issues/143), [#202](https://github.com/webpack-contrib/terser-webpack-plugin/issues/202)).

#### `Boolean`

Enable/disable multi-process parallel running.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        parallel: true,
      }),
    ],
  },
};
```

#### `Number`

Enable multi-process parallel running and set number of concurrent runs.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        parallel: 4,
      }),
    ],
  },
};
```

### `minify`

Type: `Function`
Default: `undefined`

Allows you to override default minify function.
By default plugin uses [terser](https://github.com/terser-js/terser) package.
Useful for using and testing unpublished versions or forks.

> ⚠️ **Always use `require` inside `minify` function when `parallel` option enabled**.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        terserOptions: {
          myCustomOption: true,
        },
        // Can be async
        minify: (file, sourceMap, minimizerOptions) => {
          // The `minimizerOptions` option contains option from the `terserOptions` option
          // You can use `minimizerOptions.myCustomOption`
          const extractedComments = [];

          // Custom logic for extract comments

          const { map, code } = require("uglify-module") // Or require('./path/to/uglify-module')
            .minify(file, {
              /* Your options for minification */
            });

          return { map, code, extractedComments };
        },
      }),
    ],
  },
};
```

### `terserOptions`

Type: `Object`
Default: [default](https://github.com/terser-js/terser#minify-options)

Terser minify [options](https://github.com/terser-js/terser#minify-options).

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        terserOptions: {
          ecma: undefined,
          parse: {},
          compress: {},
          mangle: true, // Note `mangle.properties` is `false` by default.
          module: false,
          // Deprecated
          output: null,
          format: null,
          toplevel: false,
          nameCache: null,
          ie8: false,
          keep_classnames: undefined,
          keep_fnames: false,
          safari10: false,
        },
      }),
    ],
  },
};
```

### `extractComments`

Type: `Boolean|String|RegExp|Function<(node, comment) -> Boolean|Object>|Object`
Default: `true`

Whether comments shall be extracted to a separate file, (see [details](https://github.com/webpack/webpack/commit/71933e979e51c533b432658d5e37917f9e71595a)).
By default extract only comments using `/^\**!|@preserve|@license|@cc_on/i` regexp condition and remove remaining comments.
If the original file is named `foo.js`, then the comments will be stored to `foo.js.LICENSE.txt`.
The `terserOptions.format.comments` option specifies whether the comment will be preserved, i.e. it is possible to preserve some comments (e.g. annotations) while extracting others or even preserving comments that have been extracted.

#### `Boolean`

Enable/disable extracting comments.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        extractComments: true,
      }),
    ],
  },
};
```

#### `String`

Extract `all` or `some` (use `/^\**!|@preserve|@license|@cc_on/i` RegExp) comments.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        extractComments: "all",
      }),
    ],
  },
};
```

#### `RegExp`

All comments that match the given expression will be extracted to the separate file.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        extractComments: /@extract/i,
      }),
    ],
  },
};
```

#### `Function<(node, comment) -> Boolean>`

All comments that match the given expression will be extracted to the separate file.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        extractComments: (astNode, comment) => {
          if (/@extract/i.test(comment.value)) {
            return true;
          }

          return false;
        },
      }),
    ],
  },
};
```

#### `Object`

Allow to customize condition for extract comments, specify extracted file name and banner.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        extractComments: {
          condition: /^\**!|@preserve|@license|@cc_on/i,
          filename: (fileData) => {
            // The "fileData" argument contains object with "filename", "basename", "query" and "hash"
            return `${fileData.filename}.LICENSE.txt${fileData.query}`;
          },
          banner: (licenseFile) => {
            return `License information can be found in ${licenseFile}`;
          },
        },
      }),
    ],
  },
};
```

##### `condition`

Type: `Boolean|String|RegExp|Function<(node, comment) -> Boolean|Object>`

Condition what comments you need extract.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        extractComments: {
          condition: "some",
          filename: (fileData) => {
            // The "fileData" argument contains object with "filename", "basename", "query" and "hash"
            return `${fileData.filename}.LICENSE.txt${fileData.query}`;
          },
          banner: (licenseFile) => {
            return `License information can be found in ${licenseFile}`;
          },
        },
      }),
    ],
  },
};
```

##### `filename`

Type: `String|Function<(string) -> String>`
Default: `[file].LICENSE.txt[query]`

Available placeholders: `[file]`, `[query]` and `[filebase]` (`[base]` for webpack 5).

The file where the extracted comments will be stored.
Default is to append the suffix `.LICENSE.txt` to the original filename.

> ⚠️ We highly recommend using the `txt` extension. Using `js`/`cjs`/`mjs` extensions may conflict with existing assets which leads to broken code.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        extractComments: {
          condition: /^\**!|@preserve|@license|@cc_on/i,
          filename: "extracted-comments.js",
          banner: (licenseFile) => {
            return `License information can be found in ${licenseFile}`;
          },
        },
      }),
    ],
  },
};
```

##### `banner`

Type: `Boolean|String|Function<(string) -> String>`
Default: `/*! For license information please see ${commentsFile} */`

The banner text that points to the extracted file and will be added on top of the original file.
Can be `false` (no banner), a `String`, or a `Function<(string) -> String>` that will be called with the filename where extracted comments have been stored.
Will be wrapped into comment.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        extractComments: {
          condition: true,
          filename: (fileData) => {
            // The "fileData" argument contains object with "filename", "basename", "query" and "hash"
            return `${fileData.filename}.LICENSE.txt${fileData.query}`;
          },
          banner: (commentsFile) => {
            return `My custom banner about license information ${commentsFile}`;
          },
        },
      }),
    ],
  },
};
```

## Examples

### Preserve Comments

Extract all legal comments (i.e. `/^\**!|@preserve|@license|@cc_on/i`) and preserve `/@license/i` comments.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        terserOptions: {
          format: {
            comments: /@license/i,
          },
        },
        extractComments: true,
      }),
    ],
  },
};
```

### Remove Comments

If you avoid building with comments, use this config:

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        terserOptions: {
          format: {
            comments: false,
          },
        },
        extractComments: false,
      }),
    ],
  },
};
```

### Custom Minify Function

Override default minify function - use `uglify-js` for minification.

**webpack.config.js**

```js
module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        minify: (file, sourceMap) => {
          // https://github.com/mishoo/UglifyJS2#minify-options
          const uglifyJsOptions = {
            /* your `uglify-js` package options */
          };

          if (sourceMap) {
            uglifyJsOptions.sourceMap = {
              content: sourceMap,
            };
          }

          return require("uglify-js").minify(file, uglifyJsOptions);
        },
      }),
    ],
  },
};
```

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