namae/api/services/slack/[query].ts

import {send, sendError, fetch} from '../../../util/http';
import {NowRequest, NowResponse} from '@vercel/node';

export default async function handler(
  req: NowRequest,
  res: NowResponse,
): Promise<void> {
  const {query} = req.query;

  if (!query || typeof query !== 'string') {
    return sendError(res, new Error('No query given'));
  }

  if (/[^a-zA-Z0-9_-]/.test(query)) {
    return sendError(res, new Error('Invalid characters'));
  }

  try {
    const response = await fetch(
      `https://${encodeURIComponent(query)}.slack.com`,
    );
    const availability = response.status !== 200;
    send(res, {availability});
  } catch (err) {
    sendError(res, err);
  }
}