Convert to type: module

Convert to native ECMAScript Modules, supported since Node.js 12.17.
This gains the benefits of native `import`/`export` for faster
asynchronous loading, cycle detection, and tree shaking in bundlers.
Unfortunately, it will create some pain for dependencies, since ESM can
not be imported using `require()` and must be imported using `import()`,
which operates asynchronously and returns a `Promise`.

See discussion in sindresorhus/meta#15

Signed-off-by: Kevin Locke <kevin@kevinlocke.name>

.eslintrc.json

@@ -23,6 +23,9 @@
         "bin/*.js"
       ],
       "rules": {
+        // Executable scripts are not expected to have exports
+        "import/no-unused-modules": "off",
+
         // Executable scripts should have a shebang
         "node/shebang": "off"
       }

.github/workflows/node.js.yml

@@ -69,7 +69,7 @@ jobs:
         - ubuntu-latest
         - windows-latest
         node:
-        - '10.17'
+        - '12.17'
         - '*'
         exclude:
         # Exclude os/version already run in test-primary

bin/cmd.js

@@ -4,9 +4,7 @@
  * @license MIT
  */
 
-'use strict';
-
-const main = require('../cli.js');
+import main from '../cli.js';
 
 // This file was invoked directly.
 // Note:  Could pass process.exit as callback to force immediate exit.

cli.js

@@ -4,16 +4,14 @@
  * @module modulename/cli.js
  */
 
-'use strict';
+import { Command } from 'commander';
+// TODO [engine:node@>=14]: Use readFile from 'fs/promises'
+import { promises as fsPromises } from 'fs';
 
-const { Command } = require('commander');
-// https://github.com/mysticatea/eslint-plugin-node/issues/174
-// eslint-disable-next-line node/no-unsupported-features/node-builtins
-const { readFile } = require('fs').promises;
-const path = require('path');
+import modulename from './index.js';
+import { modulenameMockSymbol } from './lib/symbols.js';
 
-const modulename = require('.');
-const { modulenameMockSymbol } = require('./lib/symbols.js');
+const { readFile } = fsPromises;
 
 /** Option parser to count the number of occurrences of the option.
  *
@@ -55,7 +53,7 @@ async function readJson(pathOrUrl, options) {
  * @returns {!Promise<number>} Promise for exit code.  Only rejected for
  * arguments with invalid type (or args.length < 2).
  */
-async function modulenameMain(args, options) {
+export default async function modulenameMain(args, options) {
   if (!Array.isArray(args) || args.length < 2) {
     throw new TypeError('args must be an Array with at least 2 items');
   }
@@ -105,7 +103,7 @@ async function modulenameMain(args, options) {
 
   if (argOpts.version) {
     const packageJson =
-      await readJson(path.join(__dirname, 'package.json'));
+      await readJson(new URL('package.json', import.meta.url));
     options.stdout.write(`${packageJson.version}\n`);
     return 0;
   }
@@ -123,5 +121,3 @@ async function modulenameMain(args, options) {
     return 1;
   }
 }
-
-module.exports = modulenameMain;

index.js

@@ -4,13 +4,10 @@
  * @module modulename
  */
 
-'use strict';
-
-module.exports =
-async function func(options) {
+export default async function func(options) {
   if (options !== undefined && typeof options !== 'object') {
     throw new TypeError('options must be an object');
   }
 
   // Do stuff
-};
+}

lib/symbols.js

@@ -6,10 +6,9 @@
  * This file is intentionally excluded from package.json#exports.
  */
 
-'use strict';
-
 /** Symbol of mock function used in place of modulename for testing.
  *
  * @private
  */
-exports.modulenameMockSymbol = Symbol('modulenameMock');
+// eslint-disable-next-line import/prefer-default-export
+export const modulenameMockSymbol = Symbol('modulename');

package.json

@@ -14,14 +14,13 @@
     "type": "git",
     "url": "https://github.com/kevinoid/node-project-template.git"
   },
-  "type": "commonjs",
+  "type": "module",
   "files": [
     "*.js",
     "bin/",
     "lib/",
     "!**/.*"
   ],
-  "main": "index.js",
   "exports": {
     ".": "./index.js",
     "./package.json": "./package.json"
@@ -72,7 +71,7 @@
     "rimraf": "^3.0.0"
   },
   "engines": {
-    "node": ">=10.17",
+    "node": ">=12.17",
     "npm": ">=1.3.7"
   },
   "david": {

test/.eslintrc.json

@@ -11,6 +11,9 @@
     // Braces around body of it() function is more consistent/readable
     "arrow-body-style": "off",
 
+    // Tests are not expected to have exports
+    "import/no-unused-modules": "off",
+
     // Allow null use in tests
     "unicorn/no-null": "off"
   }

test/cli.js

@@ -3,20 +3,18 @@
  * @license MIT
  */
 
-'use strict';
+import assert from 'assert';
+// TODO [engine:node@>=14]: Use readFile from 'fs/promises'
+import { promises as fsPromises } from 'fs';
+import { PassThrough } from 'stream';
 
-const assert = require('assert');
-// https://github.com/mysticatea/eslint-plugin-node/issues/174
-// eslint-disable-next-line node/no-unsupported-features/node-builtins
-const { readFile } = require('fs').promises;
-const path = require('path');
-const { PassThrough } = require('stream');
+import main from '../cli.js';
+import { modulenameMockSymbol } from '../lib/symbols.js';
 
-const main = require('../cli.js');
-const { modulenameMockSymbol } = require('../lib/symbols.js');
+const { readFile } = fsPromises;
 
 const packageJsonPromise =
-  readFile(path.join(__dirname, '..', 'package.json'), { encoding: 'utf8' })
+  readFile(new URL('../package.json', import.meta.url), { encoding: 'utf8' })
     .then(JSON.parse);
 
 const sharedArgs = ['node', 'modulename'];

test/index.js

@@ -3,9 +3,7 @@
  * @license MIT
  */
 
-'use strict';
-
-const modulename = require('..');
+import modulename from '../index.js';
 
 describe('modulename', () => {
   it('does something', (done) => {