cli.js

#!/usr/bin/env node
const fs = require("fs");
const path = require("path");

const { convertTemplateToJavaScript } = require("./index");

let args = process.argv.slice(2);

let projectDir = path.resolve(args[0]);

convertTemplateToJavaScript(projectDir)
  .then(() => {
    process.exit(0);
  })
  .catch((error) => {
    console.error(error);
    process.exit(1);
  });

index.js

const path = require("path");
const fse = require("fs-extra");
const glob = require("fast-glob");
const babel = require("@babel/core");
const babelPluginSyntaxJSX = require("@babel/plugin-syntax-jsx");
const babelPresetTypeScript = require("@babel/preset-typescript");
const prettier = require("prettier");

function convertToJavaScript(
  filename,
  source,
  projectDir
) {
  let result = babel.transformSync(source, {
    filename,
    presets: [[babelPresetTypeScript, { jsx: "preserve" }]],
    plugins: [babelPluginSyntaxJSX],
    compact: false,
    retainLines: true,
    cwd: projectDir,
  });

  if (!result || !result.code) {
    throw new Error("Could not parse typescript");
  }

  /*
    Babel's `compact` and `retainLines` options are both bad at formatting code.
    Use Prettier for nicer formatting.
  */
  return prettier.format(result.code, { parser: "babel" });
}

async function convertTemplateToJavaScript(projectDir) {
  // 1. Convert all .ts files in the template to .js
  let entries = glob.sync("**/*.+(ts|tsx)", {
    cwd: projectDir,
    absolute: true,
    ignore: ["**/node_modules/**"],
  });
  for (let entry of entries) {
    if (entry.endsWith(".d.ts")) {
      fse.removeSync(entry);
      continue;
    }

    let contents = fse.readFileSync(entry, "utf8");
    let filename = path.basename(entry);
    let javascript = convertToJavaScript(filename, contents, projectDir);

    fse.writeFileSync(entry, javascript, "utf8");
    if (entry.endsWith(".tsx")) {
      fse.renameSync(entry, entry.replace(/\.tsx?$/, ".jsx"));
    } else {
      fse.renameSync(entry, entry.replace(/\.ts?$/, ".js"));
    }
  }

  // 2. Rename the tsconfig.json to jsconfig.json
  if (fse.existsSync(path.join(projectDir, "tsconfig.json"))) {
    fse.renameSync(
      path.join(projectDir, "tsconfig.json"),
      path.join(projectDir, "jsconfig.json")
    );
  }

  // 3. Remove @types/* and typescript from package.json
  let packageJsonPath = path.join(projectDir, "package.json");
  if (!fse.existsSync(packageJsonPath)) {
    throw new Error("Could not find package.json");
  }
  let pkg = JSON.parse(fse.readFileSync(packageJsonPath, "utf8"));
  let devDeps = pkg.devDependencies || {};
  devDeps = Object.fromEntries(
    Object.entries(devDeps).filter(([name]) => {
      return !name.startsWith("@types/") && name !== "typescript";
    })
  );
  pkg.devDependencies = devDeps;
  fse.writeJSONSync(packageJsonPath, pkg, {
    spaces: 2,
  });
}

package.json

{
  "name": "@mcansh/untype",
  "version": "1.0.0",
  "bin": "./cli.js",
  "license": "MIT",
  "dependencies": {
    "@babel/core": "7.17.8",
    "@babel/plugin-syntax-jsx": "7.16.7",
    "@babel/preset-typescript": "7.16.7",
    "fast-glob": "3.2.11",
    "fs-extra": "10.0.1",
    "prettier": "2.6.1"
  }
}