text: const babel = require("gulp-babel");
  const del = require("del");
  const gulp = require("gulp");
  const runSequence = require("run-sequence");
  const watch = require("gulp-watch");
  
  const SRC_ROOT = "./src";
  const LIB_ROOT = "./lib";
  
  gulp.task("default", [ "build" ]);
  gulp.task("dev", [ "build:watch" ]);
  
  gulp.task("clean", cb => {
      del(`${LIB_ROOT}`).then(() => {
          cb()
      }, reason => {
          cb(reason);
      });
  });
  
  gulp.task("build", [ "clean" ], cb => {
      return gulp.src(`${SRC_ROOT}/**/*.js`)
          .pipe(babel())
          .pipe(gulp.dest(`${LIB_ROOT}`));
  });
  
  gulp.task("build:watch", [ "build" ], cb => {
      const jsPath = `${SRC_ROOT}/**/*.js`;
      return gulp.src(jsPath)
          .pipe(watch(jsPath))
          .pipe(babel())
          .pipe(gulp.dest(`${LIB_ROOT}`));
  });
  