ft/aurelia_project/tasks/transpile.js

import gulp from 'gulp';
import changedInPlace from 'gulp-changed-in-place';
import plumber from 'gulp-plumber';
import babel from 'gulp-babel';
import sourcemaps from 'gulp-sourcemaps';
import notify from 'gulp-notify';
import rename from 'gulp-rename';
import project from '../aurelia.json';
import {CLIOptions, build} from 'aurelia-cli';
// import debug from 'gulp-debug';

function configureEnvironment() {
  let env = CLIOptions.getEnvironment();

  return gulp.src(`aurelia_project/environments/${env}.js`)
    .pipe(changedInPlace({firstPass: true}))
    .pipe(rename('environment.js'))
    .pipe(gulp.dest(project.paths.root));
}

function buildJavaScript() {
    // TODO: should lintJS run here instead of in the build task?
  return gulp.src(project.transpiler.source)
    // .pipe(debug({title: 'start transpile:'}))
    .pipe(plumber({errorHandler: notify.onError('Error: <%= error.message %>')}))
    .pipe(changedInPlace({firstPass: true}))
    .pipe(sourcemaps.init())
    .pipe(babel(project.transpiler.options))
    .pipe(build.bundle());
}

export default gulp.series(
  configureEnvironment,
  buildJavaScript
);