var downloadLink      = document.createElement('a');
downloadLink.target   = '_blank';
downloadLink.download = 'name_to_give_saved_file.pdf';

// convert downloaded data to a Blob
var blob = new Blob(['downloadedFile'], { type: 'application/pdf' });

// create an object URL from the Blob
var URL = window.URL || window.webkitURL;
var downloadUrl = URL.createObjectURL(blob);

// set object URL as the anchor's href
downloadLink.href = downloadUrl;

// append the anchor to document body
document.body.append(downloadLink);

// fire a click event on the anchor
downloadLink.click();