feat(json): Add extensions option to load JSON files with custom extensions.

packages/json/README.md

@@ -103,6 +103,12 @@ Default: `false`
 
 If `true`, instructs the plugin to declare properties as variables, using either `var` or `const`. This pertains to tree-shaking.
 
+### `extensions`
+
+Type: `Array[...String]`<br>
+Default: `['.json']`
+A list of file extensions to be handled by the plugin. By default, only `.json` files are handled.
+
 ## Meta
 
 [CONTRIBUTING](/.github/CONTRIBUTING.md)

packages/json/src/index.js

@@ -1,15 +1,19 @@
 import { createFilter, dataToEsm } from '@rollup/pluginutils';
+import { extname } from 'path';
 
 export default function json(options = {}) {
   const filter = createFilter(options.include, options.exclude);
   const indent = 'indent' in options ? options.indent : '\t';
+  const extensions = new Set('extensions' in options ? options.extensions : ['.json']);
 
   return {
     name: 'json',
 
     // eslint-disable-next-line no-shadow
     transform(code, id) {
-      if (id.slice(-5) !== '.json' || !filter(id)) return null;
+      const extension = extname(id);
+
+      if (!extensions.has(extension) || !filter(id)) return null;
 
       try {
         const parsed = JSON.parse(code);

packages/json/test/fixtures/custom-file-extension/config.customjson

@@ -0,0 +1,3 @@
+{
+  "answer": 42
+}

packages/json/test/fixtures/custom-file-extension/main.js

@@ -0,0 +1,3 @@
+import config from './config.customjson';
+
+t.is(config.answer, 42);

packages/json/test/test.js

@@ -164,3 +164,24 @@ test('handles empty keys', async (t) => {
     'export var b = "c";\nexport default {\n\t"": "a",\n\tb: b\n};\n'
   );
 });
+
+test('uses extensions option', async (t) => {
+  const bundle = await rollup({
+    input: 'fixtures/custom-file-extension/main.js',
+    plugins: [
+      json({
+        extensions: ['.customjson']
+      })
+    ]
+  });
+  t.plan(1);
+  return testBundle(t, bundle);
+});
+
+test('does not process non-custom extensions', async (t) => {
+  const content = 'some content';
+  const id = 'testfile.json';
+  const plugin = json({ extensions: ['.custom'] });
+  const output = plugin.transform(content, id);
+  t.is(output, null, 'Should return null for files without custom extensions');
+});

packages/json/types/index.d.ts

@@ -33,6 +33,11 @@ export interface RollupJsonOptions {
    * @default true
    */
   namedExports?: boolean;
+  /**
+   * Specify the file extensions to be parsed as JSON
+   * @default ['.json']
+   */
+  extensions?: string[];
 }
 
 /**