Try this code:
document.addEventListener("deviceready", onDeviceReady, false);
function onDeviceReady() {
console.log("device is ready");
window.requestFileSystem = window.requestFileSystem || window.webkitRequestFileSystem;
window.requestFileSystem(LocalFileSystem.PERSISTENT, 0, gotFS, fail);
}
function fail() {
console.log("failed to get filesystem");
}
function gotFS(fileSystem) {
console.log("got filesystem");
// save the file system for later access
console.log(fileSystem.root.fullPath);
window.rootFS = fileSystem.root;
}
function downloadImage(url, fileName){
var ft = new FileTransfer();
ft.download(
url,
window.rootFS.fullPath + "/" + fileName,
function(entry) {
console.log("download complete: " + entry.fullPath);
},
function(error) {
console.log("download error" + error.code);
}
);
}
The gist shows the implementation which works for both iOS and Android