fix: allow loading elements from js-file again

src/meta/table.spec.ts

+import path from "path";
+
 /* mock ajv for easier testing of errors and to allow invalid values though the
  * validation to ensure the code works anyway */
 interface Validate {
@@ -94,6 +96,49 @@ describe("MetaTable", () => {
 		expect(table.getMetaFor("$schema")).toBeNull();
 	});
 
+	describe("should load metadata from", () => {
+		const fileDir = path.resolve(__dirname, "../../test-files/meta");
+
+		it("json file", () => {
+			expect.assertions(1);
+			const table = new MetaTable();
+			const filename = path.join(fileDir, "elements-json.json");
+			table.loadFromFile(filename);
+			expect(table.getMetaFor("foo")).toMatchInlineSnapshot(`
+				Object {
+				  "flow": true,
+				  "tagName": "foo",
+				}
+			`);
+		});
+
+		it("js file", () => {
+			expect.assertions(1);
+			const table = new MetaTable();
+			const filename = path.join(fileDir, "elements-js.js");
+			table.loadFromFile(filename);
+			expect(table.getMetaFor("foo")).toMatchInlineSnapshot(`
+				Object {
+				  "flow": true,
+				  "tagName": "foo",
+				}
+			`);
+		});
+
+		it("js without extension", () => {
+			expect.assertions(1);
+			const table = new MetaTable();
+			const filename = path.join(fileDir, "elements-js");
+			table.loadFromFile(filename);
+			expect(table.getMetaFor("foo")).toMatchInlineSnapshot(`
+				Object {
+				  "flow": true,
+				  "tagName": "foo",
+				}
+			`);
+		});
+	});
+
 	describe("getMetaFor", () => {
 		let table: MetaTable;
 

src/meta/table.ts

-import fs from "fs";
 import Ajv from "ajv";
 import deepmerge from "deepmerge";
 import jsonMergePatch from "json-merge-patch";
@@ -137,17 +136,21 @@ export class MetaTable {
 	 * Load metadata table from filename
 	 */
 	public loadFromFile(filename: string): void {
-		let json;
 		try {
-			const data = fs.readFileSync(filename, "utf-8");
-			json = JSON.parse(data);
+			/* remove cached copy so we always load a fresh copy, important for
+			 * editors which keep a long-running instance of [[HtmlValidate]]
+			 * around. */
+			delete require.cache[require.resolve(filename)];
+
+			/* load using require as it can process both js and json */
+			const data = require(filename); // eslint-disable-line import/no-dynamic-require
+			this.loadFromObject(data, filename);
 		} catch (err) {
 			throw new UserError(
 				`Failed to load element metadata from "${filename}"`,
 				err
 			);
 		}
-		this.loadFromObject(clone(json), filename);
 	}
 
 	/**

test-files/meta/elements-js.js

+module.exports = {
+	foo: {
+		flow: true,
+	},
+};

test-files/meta/elements-json.json

+{
+  "foo": {
+    "flow": true
+  }
+}