chore: migrate to typescript

.github/workflows/tests.yml

@@ -22,5 +22,8 @@ jobs:
       - name: Install dependencies
         run: npm install
 
+      - name: Type check
+        run: npm run typecheck
+
       - name: Run tests
-        run: npm test
+        run: npm test

.gitignore

@@ -3,5 +3,6 @@
 
 coverage/
 node_modules/
+dist/
 
-.vercel
+.vercel

README.md

@@ -84,6 +84,7 @@ To get 10 languages, a dark theme, and a custom title:
 
 ### Prerequisites
 - Node.js 18+
+- TypeScript 5.0+
 - (Optional) Vercel or other Node.js hosting
 
 ### Installation

api/languages/index.js → api/languages/index.ts

@@ -1,11 +1,15 @@
-import { parseQueryParams } from "../../src/utils/params.js";
+import { parseQueryParams, type QueryParams } from "../../src/utils/params.js";
 import { fetchLanguageData, processLanguageData } from "../../src/api/github.js";
 import { generateChartData } from "../../src/render/chart.js";
 import { renderSvg } from "../../src/render/svg.js";
 import { renderError } from "../../src/render/error.js";
+import type { VercelRequest, VercelResponse } from "@vercel/node";
 
-export default async function handler(req, res) {
-  const params = parseQueryParams(req.query);
+export default async function handler(
+  req: VercelRequest, 
+  res: VercelResponse
+): Promise<void> {
+  const params = parseQueryParams(req.query as QueryParams);
   const { chartType, chartTitle, width, height, count, selectedTheme, stroke, useTestData } = params;
 
   try {
@@ -19,7 +23,7 @@ export default async function handler(req, res) {
     res.setHeader("Cache-Control", "public, max-age=3600, s-maxage=3600, stale-while-revalidate=60");
     res.status(200).send(svg);
   } catch (error) {
-    const errorSvg = renderError(error.message, width, height, selectedTheme);
+    const errorSvg = renderError((error as Error).message, width, height, selectedTheme);
     res.setHeader("Content-Type", "image/svg+xml");
     res.status(500).send(errorSvg);
   }