gulpfile.babel.js

const through = require('through2');
const chalk   = require('chalk');
const newer   = require('gulp-newer');
const babel   = require('gulp-babel');
const gutil   = require('gulp-util');
const gulp    = require('gulp');
const path    = require('path');

const scripts = './packages/*/src/**/*.js';
const dest = 'packages';

let srcEx, libFragment;

if (path.win32 === path) {
  srcEx = /(packages\\[^\\]+)\\src\\/;
  libFragment = '$1\\lib\\';
} else {
  srcEx = new RegExp('(packages/[^/]+)/src/');
  libFragment = '$1/lib/';
}

export function build() {
  return gulp.src(scripts)
    .pipe(through.obj((file, enc, callback) => {
      file._path = file.path;
      file.path = file.path.replace(srcEx, libFragment);
      callback(null, file);
    }))
    .pipe(newer(dest))
    .pipe(through.obj((file, enc, callback) => {
      gutil.log('Compiling', '"' + chalk.cyan(file._path) + '"...');
      callback(null, file);
    }))
    .pipe(babel())
    .pipe(gulp.dest(dest));
}

export const watch = gulp.series(build, () => {
  gulp.watch(scripts, { debounceDelay: 200 }, build);
});

export default build;