Add the file to a formData object code example
Example: add formdata javascript
var formData = new FormData();
formData.append("username", "Groucho");
formData.append("accountnum", 123456);
formData.append("userfile", fileInputElement.files[0]);
var content = '<a id="a"><b id="b">hey!</b></a>';
var blob = new Blob([content], { type: "text/xml"});
formData.append("webmasterfile", blob);
var request = new XMLHttpRequest();
request.open("POST", "http://foo.com/submitform.php");
request.send(formData);