node_ts_loader.js

// Adapted from https://nodejs.org/dist/latest-v14.x/docs/api/esm.html#esm_transpiler_loader
import { readFileSync, writeFileSync } from 'fs'
import { dirname } from 'path'
import { URL, pathToFileURL, fileURLToPath } from 'url'
import esbuild from 'esbuild'

const baseURL = pathToFileURL(`${process.cwd()}/`).href
const tsExtensionRegex = /\.(tsx?)$/

function readJSON(path) {
	try {
		return JSON.parse(readFileSync(path))
	} catch (err) {}
}

function getPackageJSON(base = baseURL) {
	let packageJSONUrl = new URL('./package.json', base);
	while (true) {
		const packageJSONPath = packageJSONUrl.pathname;
		if (packageJSONPath.endsWith('node_modules/package.json')) {
			break
		}

    const packageConfig = readJSON(fileURLToPath(packageJSONUrl));
    if (packageConfig !== undefined) {
			return packageConfig
		}

    const lastPackageJSONUrl = packageJSONUrl;
    packageJSONUrl = new URL('../package.json', packageJSONUrl);

    if (packageJSONUrl.pathname === lastPackageJSONUrl.pathname) {
			break
		}
	}
}

export function resolve(specifier, context, defaultResolve) {
  const { parentURL = baseURL } = context

  if (tsExtensionRegex.test(specifier)) {
    return {
      url: new URL(specifier, parentURL).href
    }
	}

  return defaultResolve(specifier, context, defaultResolve)
}

export function getFormat(url, context, defaultGetFormat) {
  if (tsExtensionRegex.test(url)) {
    return {
      format: 'module'
    }
  }

  return defaultGetFormat(url, context, defaultGetFormat)
}

export function transformSource(contents, context, defaultTransformSource) {
	const { url, format } = context
	const match = url.match(tsExtensionRegex)

  if (match) {
		const sourcefile = fileURLToPath(url)
		const resolveDir = dirname(sourcefile)
		const [, loader] = match
		const pkg = getPackageJSON()
		const result = esbuild.buildSync({
			platform: 'node',
			format: 'esm',
			bundle: true,
			sourcemap: true,
			write: false,
			external: [
				...Object.keys(pkg.dependencies || {}),
				...Object.keys(pkg.devDependencies || {}),
				...Object.keys(pkg.peerDependencies || {}),
			],
			stdin: {
				contents,
				sourcefile,
				resolveDir,
				loader
			}
		})

		// Uncomment to save build output to disk
		writeFileSync('/Users/nsivertsen/Downloads/out.js', new TextDecoder("utf-8").decode(result.outputFiles[0].contents))

    return {
			source: result.outputFiles[0].contents
    }
  }

  return defaultTransformSource(contents, context, defaultTransformSource)
}