> For the complete documentation index, see [llms.txt](https://mhy.js.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mhy.js.org/recipes-and-examples/package.json-overrides.md).

# package.json overrides

Using `json-merger`'s syntax you have powerful ways to customize configs without *JavaScript* directly in your `package.json` files. There can be some really exotic cases tho. This is a place to collect some of these solutions.

All samples should be placed inside `{ "mhy": { HERE } }` in your `package.json` file.

## Extend `.npmignore` with custom file names

```json
"npmignore": {
  "root": {
    "$concat": [
      "/test",
      "/ci.sh",
      "/.gitbook"
    ]
  }
}
```

## `babel`: Deep customization

> Note: Babel support was replaced by SWC, but the example is still helpful.

1. Change `preset-env` to produce `commonjs` modules
2. Add `module.exports` statements to each module for default exports (from Babel v7 it is not being added anymore by default)
3. Remove `regenerator-plugin`, it doesn't needed in `node`.

```json
"babel": {
  "production": {
    "presets": [
      {
        "$match": {
          "query": "$[?(@[0].includes('preset-env'))]",
          "value": [
            {
              "$match": {
                "index": 1,
                "value": {
                  "modules": "commonjs",
                  "targets": {
                    "node": true,
                    "esmodules": true
                  }
                }
              }
            }
          ]
        }
      }
    ],
    "plugins": [
      {
        "$prepend": {
          "$expression": "$params.require.resolve('babel-plugin-add-module-exports')"
        }
      },
      {
        "$match": {
          "query": "$[?(@.includes('regenerator'))]",
          "value": {
            "$remove": true
          }
        }
      }
    ]
  }
}
```

## `Webpack`: Some customization

1. Generate `index.php` file instead of `index.html` (in this case `html-webpack-plugin` is the first in the plugins array).
2. Change regex for ignored modules from watch. This exact example is useful when working with locally linked npm modules and you want to recompile on it's changes also.

```json
"webpack": {
    "production": {
        "plugins": [{
            "$expression": "Object.assign($targetProperty.options, {filename : 'index.php'})"
        }]
    },
    "development": {
        "watchOptions": {
            "ignored": [
                "node_modules.(?!(my-module-.*)).*"
            ]
        }
    }
}
```

## `Jest`: Load extra environment setup file

```json
"jest": {
  "development": {
    "setupFilesAfterEnv": {
      "$concat": [
        "./test-setup.js"
      ]
    }
  }
}
```


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