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# resolve.dedupe

- **Type:** `string[]`
- **Default:** `undefined`

Force Rsbuild to resolve the specified packages from project root, which is useful for deduplicating packages and reducing the bundle size.

## Example

For example, assume your project is based on React 19, and you are using the `foo` package that depends on React 17, then your project will have two different versions of React:

```
app/
├── src/
└── node_modules/
    ├── foo/
    │   └── node_modules/
    │       ├── react (v17)
    │       └── react-dom (v17)
    ├── react (v19)
    └── react-dom (v19)
```

In this case, you can use the `resolve.dedupe` config to remove the duplicate React packages, and resolve all `react` and `react-dom` packages to `/node_modules/react` and `/node_modules/react-dom`:

```ts title="rsbuild.config.ts"
export default defineConfig({
  resolve: {
    dedupe: ['react', 'react-dom'],
  },
});
```

Note that using `resolve.dedupe` to unify different major versions of a package may cause some packages to fail because they may depend on specific versions of APIs or features.

For example, if `foo` depends on a React 17-specific API or feature, then unifying React 17 and React 19 with React 19 using `resolve.dedupe` may cause `foo` to fail.

## How it works

`resolve.dedupe` is implemented based on [resolve.alias](/config/resolve/alias.md), it will get the path of the specified package through `require.resolve` in the project root directory and set it to the alias.

In the above example, `resolve.dedupe` will be converted to the following alias config:

```ts
const alias = {
  react: '/app/node_modules/react',
  'react-dom': '/app/node_modules/react-dom',
};
```

The alias generated by `resolve.dedupe` will be merged with the configured `resolve.alias` in the project, and the `resolve.alias` config will take precedence when the keys are the same.