PDF is blank when downloading using javascript

solved it via XMLHttpRequest and xhr.responseType="arraybuffer";
code:

var xhr = new XMLHttpRequest();
    xhr.open('GET', './api/exportdoc/report_'+id, true);
    xhr.responseType="arraybuffer";
    xhr.onload = function(e) {
       if (this.status == 200) {
          var blob=new Blob([this.response], {type:"application/pdf"});
          var link=document.createElement('a');
          link.href=window.URL.createObjectURL(blob);
          link.download="Report_"+new Date()+".pdf";
          link.click();
       }
    };
xhr.send();