switched everything to ESM, abandoning CommonJS

to do:

* some tests are still red
* `loadExtension` now returns a promise, but `plugins.js` has yet to be
  updated accordingly: much of it should disappear when we get rid of
  legacy plugins
* documentation for end users
* documentation for developers: some signatures have changed (due to
  avoidance of default exports and because dynamic `import` is async)

in the process:

* avoided default exports (note that this changes a few modules'
  signature)
* replaced `promisify` with native alternatives
* replaced pseudo-sets and -maps with actual `Set` and `Map` instances
* introduce `async`/`await` where suitable - I did not, however, rewrite
  everything to use `async`/`await`
* got rid of a few obsolete workarounds
* tweaked stylistic details

Author: FND

bin/faucet

@@ -1,8 +1,7 @@
 #!/usr/bin/env node
-"use strict";
+import { faucetDispatch } from "../lib/index.js";
+import { parseCLI } from "../lib/cli.js";
 
-let faucet = require("../lib");
-let parseCLI = require("../lib/cli");
-
-let { referenceDir, config, options } = parseCLI();
-faucet(referenceDir, config, options);
+parseCLI.then(({ referenceDir, config, options }) => {
+	faucetDispatch(referenceDir, config, options);
+});

lib/cli.js

@@ -1,8 +1,6 @@
-"use strict";
-
-let readConfig = require("./config");
-let { abort, repr } = require("./util");
-let parseArgs = require("minimist");
+import { readConfig } from "./config.js";
+import { abort, repr } from "./util/index.js";
+import parseArgs from "minimist";
 
 let HELP = `
 Usage:
@@ -27,7 +25,7 @@ Options:
     serve generated files via HTTP with live reloading
 `.trim();
 
-module.exports = function parseCLI(argv = process.argv.slice(2), help = HELP) {
+export async function parseCLI(argv = process.argv.slice(2), help = HELP) {
 	argv = parseArgs(argv, {
 		boolean: ["watch", "fingerprint", "sourcemaps", "compact"],
 		alias: {
@@ -56,6 +54,6 @@ module.exports = function parseCLI(argv = process.argv.slice(2), help = HELP) {
 	}
 
 	let rootDir = process.cwd();
-	let { referenceDir, config } = readConfig(rootDir, argv.config);
+	let { referenceDir, config } = await readConfig(rootDir, argv.config);
 	return { referenceDir, config, options };
-};
+}

lib/config.js

@@ -1,11 +1,9 @@
-"use strict";
+import path from "path";
 
-let path = require("path");
-
-module.exports = function readConfig(rootDir, filepath = "faucet.config.js") {
+export async function readConfig(rootDir, filepath = "faucet.config.js") {
 	let configPath = path.resolve(rootDir, filepath);
 	return {
 		referenceDir: path.dirname(configPath),
-		config: require(configPath)
+		config: await import(configPath)
 	};
-};
+}

lib/index.js

@@ -1,14 +1,12 @@
-"use strict";
+import { liveServer, staticServer } from "./server.js";
+import { pluginsByBucket } from "./plugins.js";
+import { AssetManager } from "./manager.js";
+import { resolvePath } from "./util/resolve.js";
+import { abort, repr } from "./util/index.js";
+import { SerializedRunner } from "./util/runner.js";
+import browserslist from "browserslist";
 
-let server = require("./server");
-let { pluginsByBucket } = require("./plugins");
-let AssetManager = require("./manager");
-let resolvePath = require("./util/resolve");
-let { abort, repr } = require("./util");
-let SerializedRunner = require("./util/runner");
-let browserslist = require("browserslist");
-
-module.exports = async function faucetDispatch(referenceDir, config,
+export async function faucetDispatch(referenceDir, config,
 		{ watch, fingerprint, sourcemaps, compact, serve, liveserve }) {
 	config = await config;
 
@@ -39,7 +37,7 @@ module.exports = async function faucetDispatch(referenceDir, config,
 	runner.run();
 
 	if(watch) {
-		makeWatcher(config.watchDirs, referenceDir).
+		await makeWatcher(config.watchDirs, referenceDir).
 			on("edit", filepaths => {
 				runner.rerun(filepaths);
 			});
@@ -49,19 +47,19 @@ module.exports = async function faucetDispatch(referenceDir, config,
 		abort("ERROR: serve and liveserve must not be used together");
 	}
 	if(serve) {
-		server.static(serve, assetManager.manifest.webRoot);
+		staticServer(serve, assetManager.manifest.webRoot);
 	} else if(liveserve) {
-		server.live(liveserve, assetManager.manifest.webRoot);
+		liveServer(liveserve, assetManager.manifest.webRoot);
 	}
-};
+}
 
 function buildStep(plugins) {
 	return files => Promise.all(plugins.map(plugin => plugin(files))).
 		then(() => files);
 }
 
-function makeWatcher(watchDirs, referenceDir) {
-	let niteOwl = require("nite-owl");
+async function makeWatcher(watchDirs, referenceDir) {
+	let niteOwl = await import("nite-owl");
 
 	if(watchDirs) {
 		watchDirs = watchDirs.map(dir => resolvePath(dir, referenceDir,

lib/manager.js

@@ -1,12 +1,10 @@
-"use strict";
+import { Manifest } from "./manifest.js";
+import { createFile } from "./util/files/index.js";
+import { resolvePath } from "./util/resolve.js";
+import { reportFileStatus, abort, generateFingerprint } from "./util/index.js";
+import path from "path";
 
-let Manifest = require("./manifest");
-let createFile = require("./util/files");
-let resolvePath = require("./util/resolve");
-let { reportFileStatus, abort, generateFingerprint } = require("./util");
-let path = require("path");
-
-module.exports = class AssetManager {
+export class AssetManager {
 	constructor(referenceDir, { manifestConfig, fingerprint, exitOnError } = {}) {
 		this.referenceDir = referenceDir;
 		this.fingerprint = fingerprint;
@@ -30,9 +28,9 @@ module.exports = class AssetManager {
 		}
 
 		return createFile(filepath, data).
-			then(_ => this.manifest &&
+			then(() => this.manifest &&
 					this._updateManifest(originalPath, filepath, targetDir)).
-			then(_ => {
+			then(() => {
 				reportFileStatus(originalPath, this.referenceDir, error);
 				if(error && this.exitOnError) {
 					throw error;
@@ -57,4 +55,4 @@ module.exports = class AssetManager {
 		actualPath = path.relative(referenceDir, actualPath);
 		return this.manifest.set(originalPath, actualPath, targetDir);
 	}
-};
+}

lib/manifest.js

@@ -1,11 +1,9 @@
-"use strict";
+import { createFile } from "./util/files/index.js";
+import { resolvePath } from "./util/resolve.js";
+import { abort } from "./util/index.js";
+import path from "path";
 
-let createFile = require("./util/files");
-let resolvePath = require("./util/resolve");
-let { abort } = require("./util");
-let path = require("path");
-
-module.exports = class Manifest {
+export class Manifest {
 	constructor(referenceDir, { target, key, value, baseURI, webRoot } = {}) {
 		if(value && (baseURI || webRoot)) {
 			abort("ERROR: `value` must not be used with `baseURI` and/or `webRoot`");
@@ -52,4 +50,4 @@ module.exports = class Manifest {
 			return memo;
 		}, {});
 	}
-};
+}

lib/plugins.js

@@ -1,6 +1,4 @@
-"use strict";
-
-let { loadExtension, abort, repr } = require("./util");
+import { loadExtension, abort, repr } from "./util/index.js";
 
 // common plugins included for convenience
 let DEFAULTS = [{
@@ -22,15 +20,10 @@ let DEFAULT_KEYS = DEFAULTS.reduce((memo, plugin) => {
 }, new Set());
 let BUCKETS = new Set(["static", "scripts", "styles", "markup"]);
 
-module.exports = {
-	pluginsByBucket,
-	_determinePlugins: determinePlugins
-};
-
 // returns plugin functions grouped by bucket and filtered by relevance (based
 // on configuration)
-function pluginsByBucket(config, defaults) {
-	let plugins = determinePlugins(config.plugins, defaults);
+export function pluginsByBucket(config, defaults) {
+	let plugins = _determinePlugins(config.plugins, defaults);
 	let buckets = [...BUCKETS].reduce((memo, bucket) => {
 		memo[bucket] = [];
 		return memo;
@@ -61,7 +54,7 @@ function pluginsByBucket(config, defaults) {
 // `plugins` is an array of plugins, each either a package identifier or a
 // `{ key, bucket, plugin }` object`, with `key` being the configuration key and
 // `plugin` being either a function or a package identifier
-function determinePlugins(plugins = [], defaults = DEFAULTS) {
+export function _determinePlugins(plugins = [], defaults = DEFAULTS) {
 	if(!plugins.pop) { // for backwards compatibility
 		plugins = modernize(plugins);
 	}

lib/server.js

@@ -1,30 +1,28 @@
-let { loadExtension, abort, repr } = require("./util");
+import { loadExtension, abort, repr } from "./util/index.js";
 
 let DEFAULTS = {
 	host: "localhost",
 	port: 3000
 };
 
-exports.static = (config, webroot) => {
-	let donny = loadExtension("donny", "failed to activate server");
-	let [host, port] = parseHost(config);
+export async function liveServer(config, root) {
+	let server = await loadExtension("live-server", "failed to activate live-server");
+	let [host, port] = _parseHost(config);
+
+	server.start({ port, host, root, open: false });
+}
+
+export async function staticServer(config, webroot) {
+	let donny = await loadExtension("donny", "failed to activate server");
+	let [host, port] = _parseHost(config);
 
 	donny({ port, bind: host, webroot }).
 		then(() => {
 			console.error(`serving ${repr(webroot)} at http://${host}:${port}`);
 		});
-};
-
-exports.live = (config, root) => {
-	let liveServer = loadExtension("live-server", "failed to activate live-server");
-	let [host, port] = parseHost(config);
-
-	liveServer.start({ port, host, root, open: false });
-};
-
-exports._parseHost = parseHost;
+}
 
-function parseHost(config) {
+export function _parseHost(config) {
 	let { host, port } = DEFAULTS;
 	if(config === true) {
 		return [host, port];

lib/util/files/finder.js

@@ -1,11 +1,7 @@
-let fs = require("fs");
-let path = require("path");
-let { promisify } = require("util");
+import { readdir, stat } from "fs/promises";
+import path from "path";
 
-let stat = promisify(fs.stat);
-let readDir = promisify(fs.readdir);
-
-module.exports = class FileFinder {
+export class FileFinder {
 	constructor(directory, { skipDotfiles, filter = () => true } = {}) {
 		this.directory = directory;
 		this.filter = filename => {
@@ -27,7 +23,7 @@ module.exports = class FileFinder {
 		return filesWithinDirectory(this.directory, filepaths).
 			then(filepaths => filepaths.filter(this.filter));
 	}
-};
+}
 
 function tree(filepath, referenceDir = filepath) {
 	return stat(filepath).
@@ -36,7 +32,7 @@ function tree(filepath, referenceDir = filepath) {
 				return [path.relative(referenceDir, filepath)];
 			}
 
-			return readDir(filepath).
+			return readdir(filepath).
 				then(entries => {
 					let res = Promise.all(entries.map(entry => {
 						return tree(path.join(filepath, entry), referenceDir);

lib/util/files/index.js

@@ -1,42 +1,26 @@
-"use strict";
+import { writeFile } from "fs/promises";
+import { mkdirSync } from "fs";
+import path from "path";
 
-let { abort, repr } = require("../");
-let fs = require("fs");
-let path = require("path");
-let { promisify } = require("util");
-
-let KNOWN = {}; // avoids redundant `mkdirp` invocations
-let LOCKS = {};
-
-let writeFile = promisify(fs.writeFile);
+let KNOWN = new Set(); // avoids redundant `mkdir` invocations
+let LOCKS = new Map();
 
 // avoids concurrent write operations and creates target directory if necessary
-module.exports = function createFile(filepath, contents) {
-	let lock = LOCKS[filepath];
+export function createFile(filepath, contents) {
+	let lock = LOCKS.get(filepath);
 	if(lock) { // defer
-		return lock.then(_ => createFile(filepath, contents));
+		return lock.then(() => createFile(filepath, contents));
 	}
 
 	// create directory if necessary
-	if(!KNOWN[filepath]) {
-		KNOWN[filepath] = true;
-		// NB: `sync` avoids race condition for subsequent operations
-		mkdirpSync(path.dirname(filepath));
+	if(!KNOWN.has(filepath)) {
+		KNOWN.add(filepath);
+		mkdirSync(path.dirname(filepath), { recursive: true });
 	}
 
 	let prom = writeFile(filepath, contents);
-	LOCKS[filepath] = prom;
-	return prom.then(_ => {
-		delete LOCKS[filepath];
+	LOCKS.set(filepath, prom);
+	return prom.then(() => {
+		LOCKS.delete(filepath);
 	});
-};
-
-function mkdirpSync(directory) {
-	try {
-		// NB: `recursive` option was introduced in Node v10.12.0
-		fs.mkdirSync(directory, { recursive: true });
-	} catch(err) {
-		abort(`ERROR: auto-creating ${repr(directory)} requires ` +
-				"Node v10.12.0 or above");
-	}
 }