$('a#someID').attr({target: '_blank',
href : 'http://localhost/directory/file.pdf'});
function downloadURI(uri, name)
{
var link = document.createElement("a");
// If you don't know the name or want to use
// the webserver default set name = ''
link.setAttribute('download', name);
link.href = uri;
document.body.appendChild(link);
link.click();
link.remove();
}