enhance error handling for register

src/inc/routes/register.mjs

@@ -15,6 +15,9 @@ export default (router, tpl) => {
         const { username, password, password_confirm, token } = req.post;
 
         const renderError = (msg) => {
+            if (req.headers['x-requested-with'] === 'XMLHttpRequest' || (req.headers.accept && req.headers.accept.includes('application/json'))) {
+                return res.writeHead(200, { 'Content-Type': 'application/json' }).end(JSON.stringify({ success: false, msg }));
+            }
             return res.reply({
                 body: tpl.render("register", { theme: req.cookies.theme ?? "f0ck", error: msg })
             });