//Url of the file that need to be downloaded
var downloadingFileUrl = "Url of the file that need to be downloaded"
 
//File path where downloaded file will be saved
var fileSavingPath = Titanium.Filesystem.getFile(Titanium.Filesystem.applicationDataDirectory,"file_Path");
 
//Define the http client
var myHttpClient = Ti.Network.createHTTPClient();
 
//On success of downloading
myHttpClient.onload = function(){
 
   //Write the file to the desired path
    fileSavingPath.write(httpClient.responseData);
};
 
//Open the url to download
myHttpClient.open("GET",  downloadingFileUrl);
 
//Send request
myHttpClient.send(null);