swc core transform and minify: working versions (tested 2026-10-17)

{
  "name": "swc-core-transform-minify",
  "private": true,
  "type": "module",
  "scripts": {
    "test": "node --import tsx --test test/*.test.ts"
  },
  "dependencies": {
    "@swc/core": "1.16.18"
  },
  "devDependencies": {
    "@types/node": "26.6.5",
    "tsx": "4.23.15"
  }
}

import type { Options } from "@swc/core";

export const TSX_SOURCE = `type Props = { name: string; age: number };
function Greeting(props: Props) {
  const label: string = "Hello " + props.name;
  return <div className="greet">{label}</div>;
}
`;

export const PLAIN_TS_SOURCE = `function addNumbers(first: number, second: number): number {
  const total: number = first + second;
  return total;
}
(globalThis as any).__swcResult = addNumbers(20, 22);
`;

export const TSX_OPTIONS: Options = {
  jsc: {
    parser: { syntax: "typescript", tsx: true },
    target: "es2020",
  },
  module: { type: "es6" },
};

export const TS_OPTIONS: Options = {
  jsc: {
    parser: { syntax: "typescript" },
    target: "es2020",
  },
  module: { type: "es6" },
};

import { test } from "node:test";
import assert from "node:assert/strict";
import { minifySync, parseSync, transformSync } from "@swc/core";
import { PLAIN_TS_SOURCE, TSX_OPTIONS, TSX_SOURCE, TS_OPTIONS } from "../src/transform.ts";

test("strips TypeScript types from TSX input", () => {
  const { code } = transformSync(TSX_SOURCE, TSX_OPTIONS);
  assert.ok(!code.includes(": string"));
  assert.ok(!code.includes(": number"));
  assert.ok(!code.includes(": Props"));
  assert.ok(!code.includes("type Props"));
  assert.ok(code.includes("Hello"));
});

test("lowers JSX and leaves no TSX syntax", () => {
  const { code } = transformSync(TSX_SOURCE, TSX_OPTIONS);
  assert.ok(!code.includes("<div"));
  assert.ok(code.includes("createElement") || code.includes("jsx"));
});

test("parseSync returns a module AST", () => {
  const ast = parseSync(TSX_SOURCE, { syntax: "typescript", tsx: true });
  assert.equal(ast.type, "Module");
  assert.ok(Array.isArray(ast.body));
  assert.ok(ast.body.length > 0);
});

test("minifySync output is shorter and still evaluates", () => {
  const { code: compiled } = transformSync(PLAIN_TS_SOURCE, TS_OPTIONS);
  const { code: compressed } = minifySync(compiled, { compress: true, mangle: true });
  assert.ok(compressed.length < compiled.length);
  new Function(compressed)();
  assert.equal((globalThis as { __swcResult?: number }).__swcResult, 42);
  delete (globalThis as { __swcResult?: number }).__swcResult;
});