gulp.js

var util = require("util");
var Undertaker = require("undertaker");
var vfs = require("vinyl-fs");
var watch = require("glob-watcher");

function Gulp() {
  Undertaker.call(this);
  // Bind the functions for destructuring
  this.watch = this.watch.bind(this);
  this.task = this.task.bind(this);
  this.series = this.series.bind(this);
  this.parallel = this.parallel.bind(this);
  this.registry = this.registry.bind(this);
  this.tree = this.tree.bind(this);
  this.lastRun = this.lastRun.bind(this);
  this.src = this.src.bind(this);
  this.dest = this.dest.bind(this);
  this.symlink = this.symlink.bind(this);
}
util.inherits(Gulp, Undertaker);
Gulp.prototype.src = vfs.src;
Gulp.prototype.dest = vfs.dest;
Gulp.prototype.symlink = vfs.symlink;
Gulp.prototype.watch = function (glob, opt, task) {
  if (
    typeof opt === "string" ||
    typeof task === "string" ||
    Array.isArray(opt) ||
    Array.isArray(task)
  ) {
    throw new Error(
      "watching " +
        glob +
        ": watch task has to be " +
        "a function (optionally generated by using gulp.parallel " +
        "or gulp.series)"
    );
  }

  if (typeof opt === "function") {
    task = opt;
    opt = {};
  }

  opt = opt || {};

  var fn;
  if (typeof task === "function") {
    fn = this.parallel(task);
  }

  return watch(glob, opt, fn);
};
// Let people use this class from our instance
Gulp.prototype.Gulp = Gulp;

var inst = new Gulp();