Convert File into base64 in JavaScript using FileAPI

Since the File API is introduced in HTML5, we have ability to access and modify files pragramaticaly in JavaScript , here is an example of select a file using input tag and converting this binary file into base64 format.

<input type="file" id="files" name="files" />
<br/>
<textarea id="base64" rows="5"></textarea>

Checkout working example @ http://codepen.io/AshishVishwakarma/pen/pjodjV.

// Check for the File API support.
if(window.File && window.FileReader && window.FileList && window.Blob)
{
    document.getElementById('files')
        .addEventListener('change', handleFileSelect, false);
}
else
{
    alert('The File APIs are not fully supported in this browser.');
}

function handleFileSelect(evt)
{
    var f = evt.target.files[0]; // FileList object
    var reader = new FileReader();
    // Closure to capture the file information.
    reader.onload = (function (theFile)
    {
        return function (e)
        {
            var binaryData = e.target.result;
            //Converting Binary Data to base 64
            var base64String = window.btoa(binaryData);
            //showing file converted to base64
            document.getElementById('base64')
                .value = base64String;
            alert('File converted to base64 successfuly!\nCheck in Textarea');
        };
    })(f);
    // Read in the image file as a data URL.
    reader.readAsBinaryString(f);
}