003_file_to_es5.ts

import { parse } from "@babel/parser"
import * as babel from "@babel/core"
import * as fs from 'fs'

const code = fs.readFileSync('./test.js').toString()
const ast = parse(code, { sourceType: 'module' })
const result = babel.transformFromAstSync(ast, code, {
  presets: ['@babel/preset-env']
})
fs.writeFileSync('./test.es5.js', result.code)