Unplugin Compat

A plugin for legacy environments.

OXC does not support downleveling modern JavaScript syntax to ES5 and other legacy ECMAScript targets. As a result, applications built with Rolldown or Vite may not run correctly in older environments.

This plugin integrates SWC to transform and minify code for older ECMAScript targets. It includes several built-in presets and targets ES5 by default.

Currently, the plugin is distributed as an unplugin adapter and works with both Rolldown and Vite.

Installation

Install this package as a dependency in the project:

# npm
npm i unplugin-compat

# Yarn
yarn add unplugin-compat

# pnpm
pnpm add unplugin-compat

# Deno
deno add npm:unplugin-compat

# Bun
bun add unplugin-compat

Usage

Add the plugin into the Rolldown config:

import { defineConfig } from "rolldown";
import { compat } from "unplugin-compat/rolldown";

export default defineConfig({
    input: "./src/index.ts",
    plugins: [
        compat(),
    ],
});

Or add the plugin into the Vite config:

import { defineConfig } from "vite";
import { compat } from "unplugin-compat/vite";

export default defineConfig({
    plugins: [
        compat(),
    ],
});

It is possible to use the plugin with presets:

import { defineConfig } from "rolldown";
import { compat, presets } from "unplugin-compat/rolldown";

export default defineConfig({
    input: "./src/index.ts",
    plugins: [
        compat(presets.ES5),
    ],
});

Or with minifiedPresets in Vite:

import { defineConfig } from "vite";
import { compat, minifiedPresets } from "unplugin-compat/vite";

export default defineConfig({
    plugins: [
        compat(minifiedPresets.ES3),
    ],
});

Tsconfig Binding

The following tsconfig compilerOptions are automatically resolved and bound to transform options:

Compiler Options	Transform Options
jsx	jsc.parser.jsx / jsc.parser.tsx
jsxFactory	jsc.transform.react.pragma
jsxFragmentFactory	jsc.transform.react.pragmaFrag
jsxImportSource	jsc.transform.react.importSource
experimentalDecorators	jsc.parser.decorators + jsc.keepClassNames + jsc.transform.legacyDecorator
emitDecoratorMetadata	jsc.transform.decoratorMetadata
useDefineForClassFields	jsc.transform.useDefineForClassFields

Contributing

For contributing, please refer to the contributing guide.

License

This project is licensed under the terms of the MIT license.