AJAX - descarga pdf

function descargar(ruta) {

    window.URL = window.URL || window.webkitURL;  // Take care of vendor prefixes.

    var urlruta = encodeURI(ruta);

    var base_url_js = $('#base_url_js').val();

    var xhr = new XMLHttpRequest();

    xhr.open('GET', base_url_js + urlruta, true);

    xhr.responseType = 'blob';

    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 = "evaluacion.pdf";

            link.click();

        }

    };

    xhr.send();

}