Encode a file form html <input>

Hi,
when I chose  a file from an input tag of html, I have acces to an array of File object. Every File object has tihs elements:

`
{
lastModified: 42342342
lastModifiedDate: Date ...
name: "272.jpg"
size: 46675
type: "image/jpeg"
 }
`
How can I access to the file and do a `$base64.encode(file)` of it's data?
