If you want to save image from url, you have to merge the following code to you js file

First of all, we have to add the following plug-in to read, write and navigate file system.
Write this in your code:

cordova plugin add org.apache.cordova.file
cordova plugin ls

Secondly, we have to check the parameters mismatch:

function DownloadFile(URL, Folder_Name, File_Name) {
if (URL == null && Folder_Name == null && File_Name == null) {
    return;
} else {
        download(URL, Folder_Name, File_Name);
    }
  }

Thirdly, we have to "Write permission" and "Folder Creation":

function download(URL, Folder_Name, File_Name) {
// Request the file system 
    window.requestFileSystem(LocalFileSystem.PERSISTENT, 0, fileSystemSuccess, fileSystemFail);

function fileSystemSuccess(fileSystem) {
    var download_link = encodeURI(URL);
    ext = download_link.substr(download_link.lastIndexOf('.') + 1); //Get extension of URL

    var directoryEntry = fileSystem.root; // For root path of directory
    directoryEntry.getDirectory(Folder_Name, { create: true, exclusive: false }, onDirectorySuccess, onDirectoryFail); // creating folder in sdcard
    var rootdir = fileSystem.root;
    var fp = rootdir.fullPath; // Gives Fullpath of local directory

    fp = fp + "/" + Folder_Name + "/" + File_Name + "." + ext; // fullpath and name of the file which we want to give
    // Function call to download
    filetransfer(download_link, fp);
}

function onDirectorySuccess(parent) {
    // Directory successfuly created 
}

function onDirectoryFail(error) {
    // On error
    alert("Unable to create new directory: " + error.code);
}

  function fileSystemFail(evt) {
    //Unable to access file system
    alert(evt.target.error.code);
 }
}

Fourthly, We have to download a file into created folder:

function filetransfer(download_link, fp) {
var fileTransfer = new FileTransfer();
// Local path and File download function with URL
fileTransfer.download(download_link, fp,
                    function (entry) {
                        alert("download complete: " + entry.fullPath);
                    },
                 function (error) {
                     // Failed errors
                     alert("download error source " + error.source);
                 }
            );
}