Avoid using any bundlers but use tsc instead

lib/index.ts

@@ -1,5 +1,3 @@
-import { base64UrlDecode } from "./base64-url-decode.js";
-
 export interface JwtDecodeOptions {
   header?: boolean;
 }
@@ -24,6 +22,40 @@ export class InvalidTokenError extends Error {}
 
 InvalidTokenError.prototype.name = "InvalidTokenError";
 
+function b64DecodeUnicode(str: string) {
+  return decodeURIComponent(
+    atob(str).replace(/(.)/g, (m, p) => {
+      let code = p.charCodeAt(0).toString(16).toUpperCase();
+      if (code.length < 2) {
+        code = "0" + code;
+      }
+      return "%" + code;
+    })
+  );
+}
+
+function base64UrlDecode(str: string) {
+  let output = str.replace(/-/g, "+").replace(/_/g, "/");
+  switch (output.length % 4) {
+    case 0:
+      break;
+    case 2:
+      output += "==";
+      break;
+    case 3:
+      output += "=";
+      break;
+    default:
+      throw new Error("base64 string is not of the correct length");
+  }
+
+  try {
+    return b64DecodeUnicode(output);
+  } catch (err) {
+    return atob(output);
+  }
+}
+
 export function jwtDecode<T = JwtHeader>(
   token: string,
   options: JwtDecodeOptions & { header: true }