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

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

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://api.twitter.com/i/users/username_available.json?username=${query}`,
      'GET'
    ).then((res) => res.json())
    const availability = response.valid
    send(res, { availability })
  } catch (err) {
    sendError(res, err)
  }
}