Add mjs support (#30)

* Add mjs support

* FIx typos

config/node-13-exports.js

@@ -0,0 +1,15 @@
+const fs = require('fs');
+
+const snakeCaseToCamelCase = str =>
+	str.replace(/([-_][a-z])/g, group => group.toUpperCase().replace('-', ''));
+
+const copy = name => {
+	// Copy .module.js --> .mjs for Node 13 compat.
+	const filename = name.includes('-') ? snakeCaseToCamelCase(name) : name;
+	fs.writeFileSync(
+		`${process.cwd()}/dist/${filename}.mjs`,
+		fs.readFileSync(`${process.cwd()}/dist/${filename}.module.js`)
+	);
+};
+
+copy('index');

package.json

@@ -6,6 +6,14 @@
   "module": "dist/index.module.js",
   "umd:main": "dist/index.umd.js",
   "source": "src/index.js",
+  "exports": {
+		".": {
+ 			"browser": "./dist/index.module.js",
+			"umd": "./dist/index.umd.js",
+			"import": "./dist/index.mjs",
+			"require": "./dist/index.js"
+		}
+  },
   "types": "typings/index.d.ts",
   "files": [
     "dist",
@@ -31,7 +39,8 @@
     "build:clean": "rimraf dist",
     "build:bundle": "microbundle -i src/index.js --external preact --compress --strict --name preactSsrPrepass",
     "build:flow": "flow-copy-source -i '*.test.js' src/ dist/",
-    "prepublishOnly": "npm run test && npm run build"
+    "prepublishOnly": "npm run test && npm run build",
+    "postbuild": "node ./config/node-13-exports.js"
   },
   "peerDependencies": {
     "preact": ">=10 || ^10.0.0-beta.0 || ^10.0.0-alpha.0"