fix(types): export LanguageType utility type (#374)

Fixes #373

Author: metonym

README.md

@@ -334,6 +334,22 @@ Refer to the highlight.js [language definition guide](https://highlightjs.readth
 <Highlight {language} code="..." />
 ```
 
+If you're using TypeScript, use the `LanguageType` interface to type the language.
+
+```ts
+import type { LanguageType } from "svelte-highlight";
+
+const language: LanguageType<"custom-language"> = {
+  name: "custom-language",
+  register: (hljs) => {
+    return {
+      /** custom language rules */
+      contains: [],
+    };
+  },
+};
+```
+
 ## Custom Plugin
 
 Additional plugin languages can be installed and used separately.

src/index.d.ts

@@ -2,3 +2,4 @@ export { default as Highlight, default as default } from "./Highlight.svelte";
 export { default as HighlightAuto } from "./HighlightAuto.svelte";
 export { default as HighlightSvelte } from "./HighlightSvelte.svelte";
 export { default as LineNumbers } from "./LineNumbers.svelte";
+export type { LanguageType } from "./languages";

tests/languages.test.ts

@@ -1,4 +1,5 @@
 import * as languages from "../src/languages";
+import type { LanguageType } from "svelte-highlight";
 
 test("Languages", () => {
   const languageNames = Object.keys(languages);
@@ -8,3 +9,21 @@ test("Languages", () => {
   expect(languageNames.length).toEqual(192);
   expect(languageNames).toMatchSnapshot();
 });
+
+test("LanguageType", () => {
+  const language: LanguageType<"custom-language"> = {
+    name: "custom-language",
+    register: () => {
+      return {
+        contains: [],
+        tokenize: () => {
+          return {
+            tokens: [],
+          };
+        },
+      };
+    },
+  };
+
+  expect(language).toBeTruthy();
+});