i have correct my Code and it works now.
Order.prototype._downloadDetails = function () {
var sServiceUrl = _oController.getServiceUrl();
let iRoleId = _oController.getRoleId();
let iObjectId = _oController.getObjectId();
if (sServiceUrl && iRoleId && iObjectId) {
window.open(sServiceUrl
+"/download?"
+ "roleId=" + iRoleId
+ "&objectId=" + iObjectId, '_blank').focus()
}
};