Switch UMD to .js

Fixes #135

Co-authored-by: Jake Archibald <jaffathecake@gmail.com>

Author: jcubic

README.md

@@ -45,12 +45,12 @@ Legacy builds:
 
 - `idb-keyval/dist/compat.js` EcmaScript module, transpiled for older browsers.
 - `idb-keyval/dist/compat.cjs` CommonJS module, transpiled for older browsers.
-- `idb-keyval/dist/umd.cjs` UMD module, also transpiled for older browsers.
+- `idb-keyval/dist/umd.js` UMD module, also transpiled for older browsers.
 
 These built versions are also available on jsDelivr, e.g.:
 
 ```html
-<script src="https://cdn.jsdelivr.net/npm/idb-keyval@6/dist/umd.cjs"></script>
+<script src="https://cdn.jsdelivr.net/npm/idb-keyval@6/dist/umd.js"></script>
 <!-- Or in modern browsers: -->
 <script type="module">
   import { get, set } from 'https://cdn.jsdelivr.net/npm/idb-keyval@6/+esm';

rollup.config.js

@@ -135,7 +135,7 @@ export default async function ({ watch }) {
       plugins: [simpleTS('src', { noBuild: true }), commonjs(), resolve()],
       output: [
         {
-          file: 'dist/umd.cjs',
+          file: 'dist/umd.js',
           format: 'umd',
           name: 'idbKeyval',
           plugins: [
@@ -144,6 +144,18 @@ export default async function ({ watch }) {
             terser({
               compress: { ecma: 5 },
             }),
+            {
+              // jsDelivr does not serve the correct mimetype for .cjs files.
+              // However, the cjs version is retained for backwards compatibility.
+              // TODO: Remove this in the next major version.
+              generateBundle(_, bundle) {
+                this.emitFile({
+                  type: 'asset',
+                  fileName: 'umd.cjs',
+                  source: bundle['umd.js'].code,
+                });
+              },
+            },
           ],
         },
       ],