Download pdf file from ajax response

Any idea on how to optimize it for all modern browsers?

Yes, I can give you a solution tested on windows 10 with IE11, Firefox 47 and Chrome 52. Nothing for Microsoft Edge at the moment.

At the beginning you need to distinguish if you are on IE or the other two browsers. This because on IE11 you can use:

window.navigator.msSaveBlob(req.response, "PdfName-" + new Date().getTime() + ".pdf");

For the other two browsers your code works on Chrome but not on Firefox because you did not append the element to the document body.

So the corrected code is:

var req = new XMLHttpRequest();
req.open("POST", "/servicepath/Method?ids=" + ids, true);
req.responseType = "blob";
req.onreadystatechange = function () {
  if (req.readyState === 4 && req.status === 200) {

    // test for IE

    if (typeof window.navigator.msSaveBlob === 'function') {
      window.navigator.msSaveBlob(req.response, "PdfName-" + new Date().getTime() + ".pdf");
    } else {
      var blob = req.response;
      var link = document.createElement('a');
      link.href = window.URL.createObjectURL(blob);
      link.download = "PdfName-" + new Date().getTime() + ".pdf";

      // append the link to the document body

      document.body.appendChild(link);

      link.click();
    }
  }
};
req.send();

This version will work in all modern browsers:

var req = new XMLHttpRequest();
req.open("POST", "/servicepath/Method?ids=" + ids, true);
req.responseType = "blob";
req.onreadystatechange = function () {
    if (req.readyState === 4 && req.status === 200) {
        var filename = "PdfName-" + new Date().getTime() + ".pdf";
        if (typeof window.chrome !== 'undefined') {
            // Chrome version
            var link = document.createElement('a');
            link.href = window.URL.createObjectURL(req.response);
            link.download = "PdfName-" + new Date().getTime() + ".pdf";
            link.click();
        } else if (typeof window.navigator.msSaveBlob !== 'undefined') {
            // IE version
            var blob = new Blob([req.response], { type: 'application/pdf' });
            window.navigator.msSaveBlob(blob, filename);
        } else {
            // Firefox version
            var file = new File([req.response], filename, { type: 'application/force-download' });
            window.open(URL.createObjectURL(file));
        }
    }
};
req.send();

I was trying to get also a version for safari but it didn't work so well. Will try to keep investigate it and give a solution for that too.