React & JavaScript

Set the form's submit behaviour to JSON, then post with fetch. Send Accept: application/json so you always get a JSON response.

async function onSubmit(e) {
  e.preventDefault();
  const data = Object.fromEntries(new FormData(e.target));

  const res = await fetch("https://senduler.com/f/your-key", {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      "Accept": "application/json",
    },
    body: JSON.stringify(data),
  });

  if (res.ok) {
    // { ok: true, id: "..." }
    setSent(true);
  }
}

Allowed origins

Lock a form to your domain(s) in Settings → Allowed origins. Cross-origin requests from anywhere else are rejected, and the browser preflight is handled for you.

File uploads

Use multipart/form-data (a normal form with an <input type="file">) and the files are stored against the submission, subject to your plan's size limits.