gulpfile.js

const gulp = require('gulp')
const babel = require('gulp-babel')
const ts = require('gulp-typescript')
const del = require('del')

gulp.task('clean', async () => {
  await del('lib/**')
  await del('es/**')
  await del('dist/**')
})

gulp.task('es', () => {
  const tsProject = ts.createProject('tsconfig.json', {
    module: 'ESNext'
  })
  return tsProject.src().pipe(tsProject()).pipe(babel()).pipe(gulp.dest('es/'))
})

gulp.task('cjs', () => {
  return gulp
    .src(['./es/**/*.js'])
    .pipe(
      babel({
        configFile: '../../.babelrc'
      })
    )
    .pipe(gulp.dest('lib/'))
})

gulp.task('declaration', () => {
  const tsProject = ts.createProject('tsconfig.json', {
    declaration: true,
    emitDeclarationOnly: true
  })
  return tsProject.src().pipe(tsProject()).pipe(gulp.dest('es/')).pipe(gulp.dest('lib/'))
})

exports.default = gulp.series('clean', 'es', 'cjs', 'declaration')