change/API! ~ add ESM module packaging (adds 'exports' to package)

- adds an ESM wrapper to provide simple ESM support (as suggested in "Node Modules at War"

* ref: [Node Modules at War](https://redfin.engineering/node-modules-at-war-why-commonjs-and-es-modules-cant-get-along-9617135eeca1) @@ <https://archive.is/zl0qg>
* ref: [yargs ~ 'Road to ESM/Deno'](yargs/yargs#1706)

package.json

@@ -23,6 +23,17 @@
 	"main": "dist/cjs/index.js",
 	"module": "dist/cjs/esm-wrapper/index.js",
 	"types": "dist/types/index.d.ts",
+	"exports": {
+		"./package.json": "./package.json",
+		".": [
+			{
+				"import": "./dist/cjs/esm-wrapper/index.js",
+				"require": "./dist/cjs/index.js",
+				"types": "./dist/types/index.d.ts"
+			},
+			"./dist/cjs/index.js"
+		]
+	},
 	"keywords": [
 		"common",
 		"cross-platform",
@@ -44,6 +55,7 @@
 		"# build # build/compile package": "",
 		"build": "run-s _:regen:build",
 		"build:cjs": "tsc -p tsconfig/tsconfig.cjs.json",
+		"build:cjs/esm": "shx mkdir -p build/cjs && shx cp -r src/esm-wrapper build/cjs",
 		"## build:esm * [2020-12-22; rivy] TS compiles to ESMs are broken due to extension mishandling (use `rollup`)": "tsc -p tsconfig/tsconfig.esm.json",
 		"build:umd": "tsc -p tsconfig/tsconfig.umd.json",
 		"build:tests": "tsc -p tsconfig/tsconfig.tests.json",

src/esm-wrapper/index.js

@@ -0,0 +1,9 @@
+/* eslint-env node */
+// # spell-checker:ignore Deno
+
+import _ from '../index.js';
+// note: not usable by `deno`;
+//   ...`deno` is unable to load (the CJS module) '../index.js' via import => `'../index.js' does not provide an export named 'default'`
+
+const default_ = _;
+export default default_;

src/esm-wrapper/package.json

@@ -0,0 +1 @@
+{"type": "module"}

src/index.ts

@@ -9,7 +9,15 @@ const haveModuleExports_ = typeof module === 'object' && module.exports;
 // ## maint ~ [2020-12-23; rivy] although tested, `nyc` is unable to instrument ESM/.mjs correctly in order show coverage for testing the *else* clause
 /* istanbul ignore else */
 if (haveModuleExports_) {
-	// enables direct require from CJS (eg, `const m = require('...');`); skipped for ESM
+	// enables direct require from CJS (eg, `const module = require('...');`), but generally disables any other exports
+	// * skipped for ESM (missing `module.exports`)
+	// * added non-enumerable '_esm!' property (as a hack) to allow full access to all exports (for testing, ...)
 	// eslint-disable-next-line functional/immutable-data
 	module.exports = default_;
+	Object.defineProperty(module.exports, '_esm!', {
+		get() {
+			return exports;
+		},
+		enumerable: false,
+	});
 }