#TypeScript

Rsbuild supports TypeScript by default, allowing you to directly use .ts and .tsx files in your project.

#TypeScript transformation

Rsbuild uses SWC by default for transforming TypeScript code to JavaScript, and also supports switching to Babel for transformation.

#Isolated modules

Unlike the native TypeScript compiler, tools like SWC and Babel compile each file separately and cannot determine whether an imported name is a type or value. When using TypeScript in Rsbuild, enable the verbatimModuleSyntax or isolatedModules option in your tsconfig.json:

• For TypeScript >= 5.0.0, use the verbatimModuleSyntax option, which enables the isolatedModules option by default:

{
  "compilerOptions": {
    "verbatimModuleSyntax": true
  }
}

• For TypeScript < 5.0.0, use the isolatedModules option:

{
  "compilerOptions": {
    "isolatedModules": true
  }
}

The isolatedModules option prevents syntax that SWC and Babel cannot compile correctly, such as cross-file type references. It guides you toward correct usage:

// Wrong
export { SomeType } from './types';

// Correct
export type { SomeType } from './types';

See SWC - Migrating from tsc for more details about the differences between SWC and tsc.

#Preset types

@rsbuild/core provides preset type definitions, including CSS files, CSS Modules, static assets, import.meta, and other types.

Create a src/env.d.ts file to reference these types:

/// <reference types="@rsbuild/core/types" />

See types.d.ts for the complete preset type definitions that Rsbuild includes.

#Type checking

When transpiling TypeScript code using tools like SWC and Babel, type checking is not performed.

To enable type checking, use the plugin @rsbuild/plugin-type-check. It runs TypeScript type checking in a separate process and uses ts-checker-rspack-plugin under the hood.

Please refer to the @rsbuild/plugin-type-check for usage instructions.

#tsconfig.json Path

Rsbuild reads the tsconfig.json file from the root directory by default. Use source.tsconfigPath to configure a custom tsconfig.json file path.

export default {
  source: {
    tsconfigPath: './tsconfig.custom.json',
  },
};

#Path extensions

When importing another module in a TypeScript module, TypeScript allows using the .js file extension:

// The actual referenced module could be `./some-module.ts` or `./some-module.tsx`
import { someFn } from './some-module.js';

Rsbuild supports this feature through Rspack's extensionAlias configuration. In TypeScript projects, Rsbuild adds the following configuration by default:

const rspackConfig = {
  resolve: {
    extensionAlias: {
      '.js': ['.js', '.ts', '.tsx'],
      '.jsx': ['.jsx', '.tsx'],
    },
  },
};

This means:

• You can use the .js extension to import .ts or .tsx files.
• You can use the .jsx extension to import .tsx files.

#Decorators version

Rsbuild does not read the experimentalDecorators option in tsconfig.json, instead, it provides the decorators.version configuration to specify the decorator version.

By default, Rsbuild uses the 2022-03 version of the decorators, you can also set it to legacy to use the legacy decorators:

export default {
  source: {
    decorators: {
      version: 'legacy',
    },
  },
};