How to choose a file from a directory and copy it into local app data storage?

Question

I'm new to Windows Runtime and winjs. I want to able to open and choose a file(such as an image file) from a directory(such as usb drive) and copy it into the local app data folder. How can I do it?

HTML: input button to choose a file

<input type="file" onchange="saveFile(event)" />

Javascript: save file to local app data folder

function saveFile(event){
    var file = event.target.files[0];
    // How do I copy this file and save it to the local app data folder?
}