SWC

Overview

SWC compiles TypeScript, JSX and modern JavaScript down to a chosen target, converts module formats and minifies output. It is a native Rust binary exposed to Node.js as @swc/core, so it is much faster than Babel on large codebases. It strips types but does not type-check; run tsc --noEmit separately. Next.js uses SWC internally, and Parcel and many Vite, Jest and webpack setups use it through plugins and loaders.

Packages: @swc/core (API), @swc/cli (the swc command), @swc/jest (Jest transformer), swc-loader (webpack), @swc/helpers (runtime helpers when externalHelpers is on).

Instructions

Install and compile

npm install -D @swc/core @swc/cli chokidar   # chokidar only for -w
npx swc src/index.ts -o dist/index.js     # one file
npx swc src -d dist --strip-leading-paths # directory -> dist/index.js (without the flag the output is dist/src/index.js)
npx swc src -d dist -w                    # watch
npx swc src -d dist -C module.type=commonjs   # override a .swcrc key

.swcrc

{
  "$schema": "https://swc.rs/schema.json",
  "jsc": {
    "parser": { "syntax": "typescript", "tsx": true, "decorators": true },
    "transform": {
      "react": { "runtime": "automatic" },
      "decoratorVersion": "2022-03"
    },
    "target": "es2020"
  },
  "module": { "type": "es6" },
  "sourceMaps": true
}

• module.type is one of es6, commonjs, umd, amd, nodenext; SWC never rewrites import specifiers, so write the .js extension yourself when the output runs as ESM on Node.
• jsc.target and env (browserslist targets, env.targets, env.mode: "usage" with env.coreJs) are alternatives (setting both fails with "env and jsc.target cannot be used together"): use env for browser support matrices, jsc.target for a fixed ES version.
• jsc.paths plus jsc.baseUrl rewrite tsconfig-style path aliases at compile time.

Programmatic API

import { minify, transform } from "@swc/core";

const { code, map } = await transform(source, {
  filename: "Greeting.tsx",   // needed so .swcrc and the parser are chosen correctly
  jsc: { parser: { syntax: "typescript", tsx: true }, transform: { react: { runtime: "automatic" } }, target: "es2020" },
  module: { type: "es6" },
  sourceMaps: true,
});

const small = await minify("function add(first, second) { return first + second }", { compress: true, mangle: true });

transformSync and minifySync exist for build tools that cannot await. Prefer the async versions: they run on the thread pool.

Minify

Either set "minify": true at the top level of .swcrc with options under jsc.minify, or call minify():

{ "minify": true, "jsc": { "minify": { "compress": { "drop_console": true, "passes": 2 }, "mangle": true } } }

There is no separate swc-minify command.

Jest

npm install -D jest @swc/core @swc/jest

// jest.config.js
module.exports = {
  transform: {
    "^.+\\.(t|j)sx?$": ["@swc/jest", {
      jsc: { parser: { syntax: "typescript", tsx: true }, transform: { react: { runtime: "automatic" } } },
    }],
  },
};

If a .swcrc exists, @swc/jest reads it; passing inline options in the transform entry is the clearer route.

Examples

Example 1: Build a TypeScript library to ESM and CommonJS

Request: "Compile src to dist for both module systems, with source maps."

npx swc src -d dist/esm --strip-leading-paths -C module.type=es6 --source-maps
npx swc src -d dist/cjs --strip-leading-paths -C module.type=commonjs --source-maps
npx tsc --noEmit

Result: dist/esm/index.js and dist/cjs/index.js with .js.map files; the last command catches type errors because SWC does not.

Example 2: Minified production bundle step without console logs

Request: "Minify this React component and remove console.log."

With the .swcrc above extended by "minify": true and jsc.minify.compress.drop_console: true, npx swc src -d dist turns a component with console.log("render") into one line of mangled JavaScript using react/jsx-runtime with no console call.

Guidelines

• SWC does not type-check and does not emit .d.ts in the default setup (the experimental jsc.experimental.emitIsolatedDts needs explicit type annotations, as in TypeScript's isolatedDeclarations); keep tsc for declarations and checks.
• Without --strip-leading-paths, swc src -d dist writes to dist/src.
• With "minify": true at the top level SWC minifies every output; keep it in a production-only config (npx swc src -d dist --config-file .swcrc.prod).
• isolatedModules rules apply: re-exporting types needs export type.
• In Next.js, a custom .babelrc turns SWC off for that app; remove it unless a Babel plugin is required.
• Plugins are WebAssembly built against a specific @swc/core version range; upgrade them together.
• Speed-up figures vary by project; measure your own build instead of trusting headline multipliers.