I can't figure out how to get source maps working.

[trusktr]

Here's my gulpfile:

const gulp = require('gulp')
const babel = require('gulp-babel')
// const cached = require('gulp-cached')
const typescript = require('gulp-typescript')
const merge = require('merge-stream')
const babelConfig = require('./babel.config')
const tsConfig = require('./tsconfig.json')
const sourcemaps = require('gulp-sourcemaps')

function transpile() {
	return merge()
}

function watch(task) {
	return gulp.watch(
		['src/**/*.{js,jsx,ts,tsx}', '!src/**/*test.{js,jsx,ts,tsx}'],
		{ ignoreInitial: false },
		gulp.parallel(task)
	)
}

gulp.task('build-cjs', () => {
	const jsPipe = gulp
		.src(['src/**/*.{js,jsx}', '!src/**/*test.{js,jsx}'])
		// .pipe(cached('js')) // in watch mode, prevents rebuilding all files
		.pipe(sourcemaps.init())
		.pipe(babel(babelConfig))

		.pipe(
			babel({
				plugins: [
					'@babel/plugin-transform-modules-commonjs',
					'babel-plugin-add-module-exports',
				],
			})
		)

		// TODO source maps
		.pipe(sourcemaps.write())
		.pipe(gulp.dest('./'))

	const tsPipe = gulp
		.src(['src/**/*.{ts,tsx}', '!src/**/*test.{ts,tsx}'])
		// .pipe(cached('ts')) // in watch mode, prevents rebuilding all files
		.pipe(sourcemaps.init())
		.pipe(typescript(tsConfig.compilerOptions))
		.pipe(babel(babelConfig))

		.pipe(
			babel({
				plugins: [
					'@babel/plugin-transform-modules-commonjs',
					'babel-plugin-add-module-exports',
				],
			})
		)

		// TODO source maps
		.pipe(sourcemaps.write())
		.pipe(gulp.dest('./'))

	return merge(jsPipe, tsPipe)
})
gulp.task('watch-cjs', () => watch('build-cjs'))

There are no errors. An output file looks like this:

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.Box = exports.default = void 0;

var _Mesh = _interopRequireDefault(require("./Mesh"));

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }

class Box extends _Mesh.default {}

exports.Box = exports.default = Box;
Box.defaultElementName = 'i-box';
Box.defaultBehaviors = {
  'box-geometry': initialBehaviors => {
    return !initialBehaviors.some(b => b.endsWith('-geometry'));
  },
  'phong-material': initialBehaviors => {
    return !initialBehaviors.some(b => b.endsWith('-material'));
  }
};

I think a sourceMapUrl should appear at the bottom, along with a sibling source map? What have I done wrong?