index.js

async function foo (method, url, body) {
  if (!url) throw new Error()
  let config = {
    headers: { accept: 'application/json' }
  }
  if (method && body) {
    config.body = JSON.stringify(body)
    config.method = method
  }
  const res = await fetch(url, { config })
  if (!res.ok) throw new Error(res)
  return res.json()
}