convertkit-ajax.js

function addSubscriberToConvertKit ({firstName, email, formAction, onSuccess, onError}) {
  fetch(formAction, {
    method: "POST",
    body: JSON.stringify({
      "first_name": firstName,
      "email_address": email
    }),
    headers: {
      "Accept": "application/json",
      "Content-Type": "application/json"
    }
  })
  .then(res => res.json())
  .then(res => {
    if (res.status === "success") {
      onSuccess(res);
    } else {
      onError(res); // TIP: trigger an "invalid email" error if res.errors.fields.includes("email_address")
    }
  })
  .catch(err => {
    onError(res);
  });
}

addSubscriberToConvertKit({
  firstName: "xxxxxxx",
  email: "xxxxxxx@storylog.com",
  // create an "inline form" in ConvertKit, then paste the form's action here
  formAction: "https://app.convertkit.com/forms/xxxxxxxx/subscriptions",
  onSuccess: (res) => console.log("success", res),
  onError: (res) => console.log("error", res)
});