fetch("http://localhost:3000", {
  method: "POST",
  body: JSON.stringify({
    html: "<h1>Hello I am a PDF</h1>",
  }),
})
  .then((response) => response.blob())
  .then((blob) => {
    var url = window.URL.createObjectURL(blob);
    var a = document.createElement("a");
    a.href = url;
    a.download = "example.pdf"; // You can set the name programmatically
    document.body.appendChild(a); // we need to append the element to the dom -> otherwise it will not work in firefox
    a.click();
    a.remove(); //afterwards we remove the element
  });