typescript+babel+teser gulpfile. It grabs every `.ts` file in `src` and throws them in `dist`, and transpiles to every module format.

package.json

{
	"name": "typescript+babel+teser gulpfile",
	"license": "MIT",
	"author": {
		"email": "[email protected]",
		"name": "jaacko-torus",
		"url": "https://github.com/jaacko-torus"
	},
	"type": "module",
	"engines": {
		"node": "^16.12.0"
	},
	"scripts": {
		"dev": "tsc --watch",
		"gulp": "yarn gulp.build && yarn gulp.run",
		"gulp.build": "tsc --project gulp",
		"gulp.run": "gulp"
	},
	"devDependencies": {
		"@babel/cli": "^7.15.7",
		"@babel/core": "^7.15.8",
		"@babel/plugin-transform-modules-amd": "^7.14.5",
		"@babel/plugin-transform-modules-commonjs": "^7.15.4",
		"@babel/plugin-transform-modules-systemjs": "^7.15.4",
		"@babel/plugin-transform-modules-umd": "^7.14.5",
		"@babel/preset-env": "^7.15.8",
		"@types/gulp": "^4.0.9",
		"@types/gulp-babel": "^6.1.30",
		"@types/gulp-rename": "^2.0.1",
		"@types/gulp-sourcemaps": "^0.0.35",
		"@types/gulp-terser": "^1.2.1",
		"@types/node": "^16.11.5",
		"gulp": "^4.0.2",
		"gulp-babel": "^8.0.0",
		"gulp-cli": "^2.3.0",
		"gulp-rename": "^2.0.0",
		"gulp-sourcemaps": "^3.0.0",
		"gulp-terser": "^2.1.0",
		"gulp-typescript": "^6.0.0-alpha.1",
		"typescript": "^4.4.4"
	}
}

tsconfig.json

{
	"compilerOptions": {
		"alwaysStrict": true,
		"esModuleInterop": true,
		"module": "ESNext",
		"moduleResolution": "Node",
		"noImplicitAny": true,
		"sourceMap": true,
		"isolatedModules": true,
		"outDir": "..",
		"strict": true,
		"target": "ESNext"
	},
	"include": ["gulpfile.ts"],
	"exclude": ["node_modules"]
}

typescript+babel+teser.gulpfile.ts

/**
 * MIT License (c) 2021 Julian A Avar C
 *
 * Expected folder structure
 * 
 * project/
 * |- src/
 * |  |- index.ts
 * |  |- ...
 * |- gulp/
 * |  |- gulpfile.ts
 * |  |- tsconfig.json
 * |- dist/ - auto generated
 *    |- amd/
 *    |- cjs/
 *    |- mjs/
 *    |- sjs/
 *    |- umd/
 *
 * This will generate `.js`, `.map`, and their minified versions for every file under `src`.
 * 
 * gulp tasks
 * |- default - only compiles `.ts` and makes `.map` files
 * |- minify  - only minifies compiled and mapped files
 * |- dist    - does everything
 * |- dev     - only does default, but in watch mode
 *
 * Run `yarn gulp --tasks` for more info.
 */

import gulp from "gulp"
import sourcemaps from "gulp-sourcemaps"
import ts from "gulp-typescript"
import babel from "gulp-babel"
import terser from "gulp-terser"
import rename from "gulp-rename"

type Entry<T> = { [K in keyof T]: [K, T[K]] }[keyof T];

type TaskResult = NodeJS.ReadWriteStream;
type Task = () => TaskResult;

type TaskOptSuffix = { dirname?: string };
type TaskOptTask = { task: Task };
type TaskOpts = TaskOptSuffix & TaskOptTask;

type TaskName = string;
type TaskInfoRecord = { [taskName: TaskName]: TaskOptSuffix };
type TaskRecord = { [taskName: TaskName]: TaskOpts };

const modules: TaskInfoRecord = {
	mjs: {},
	umd: {},
	amd: {},
	commonjs: { dirname: "cjs" },
	systemjs: { dirname: "sjs" }
};

const task_default = () => {
	const taskCallback = ([moduleName, moduleInfoRecord]: Entry<TaskInfoRecord>) => {
		const tsResult = gulp
			.src(["src/**/*.ts"])
			.pipe(sourcemaps.init())
			.pipe(ts.createProject("tsconfig.json")());
		
		const applyModuleTransformation = () => moduleName === "mjs"
			? tsResult.js
			: tsResult.js.pipe(babel({
					presets: ["@babel/preset-env"],
					plugins: [`@babel/plugin-transform-modules-${moduleName}`]
			}))
		
		const babelResult : TaskResult = applyModuleTransformation()
			.pipe(rename({ dirname: moduleInfoRecord?.dirname ?? moduleName }));
		
		const taskOpts = { ...moduleInfoRecord, task: () => babelResult };
		
		return [moduleName, taskOpts] as Entry<TaskRecord>;
	}
	
	return Object.fromEntries(Object.entries(modules).map(taskCallback)) as TaskRecord;
}

const task_minify = () => {
	const taskCallback = ([moduleName, moduleOpts]: Entry<TaskRecord>) => {
		const terserResult = moduleOpts.task()
			.pipe(rename({ suffix: ".min" }))
			.pipe(terser({
				ecma: 2015,
				compress: true,
				mangle: {
					toplevel: true,
					reserved: ["lox"]
				}
			}));
		
		return [moduleName, { ...moduleOpts, task: () => terserResult }] as Entry<TaskRecord>;
	}
	
	return Object.fromEntries(Object.entries(task_default()).map(taskCallback)) as TaskRecord;
};

function series(taskNames : TaskName[]) {
	return gulp.series(taskNames.map(taskName => gulp.task(taskName)));
}

const mapAndWrite = (task : Task) => () => task().pipe(sourcemaps.write(".")).pipe(gulp.dest("dist"));

const makeTasks = (taskSetName : string, taskRecord : TaskRecord) => {
	const getTaskName = (taskName : string) => `${taskSetName}_${taskName}`
	
	Object.entries(taskRecord).map(([taskName, taskOpts]) => {
		gulp.task(getTaskName(taskName), mapAndWrite(taskOpts.task));
	});
	
	gulp.task(taskSetName, series(Object.entries(taskRecord).map(([taskName]) => getTaskName(taskName))));
}

makeTasks("default", task_default());
makeTasks("minify", task_minify());
gulp.task("dist", series(["default", "minify"]));
gulp.task("dev", () => gulp.watch("src/lox.ts", gulp.task("default")));