Rails API wrapper with Authenticity token

api.js

//This assumes the following script tag exists in
// the layout/application.html.erb head:
//<script charset="utf-8" type="text/javascript">
//  window.__APP_CONFIG__ = {};
//  __APP_CONFIG__.csrfToken = '<%= form_authenticity_token %>';
//</script>
async function api(url, method = "GET", data = {}) {
  const payload = { ...data, authenticity_token: __APP_CONFIG__.csrfToken };
  const endpoint =
    method === "GET" && payload
      ? `${url}?${new URLSearchParams(payload).toString()}`
      : url;
  const body =
    method !== "GET"
      ? JSON.stringify({
          ...payload,
          authenticity_token: __APP_CONFIG__.csrfToken
        })
      : null;
  const res = await fetch(endpoint, {
    method,
    headers: {
      Accept: "application/json",
      "Content-Type": "application/json"
    },
    body
  });

  return res.json();
}

export default api;