Javascript decimal to base 64 converter

gistfile1.js

// this alphabet will convert an Instagram photo ID to the base 64 number used in the URLs
// however, be wary of javascript's maxint value
alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_';

function b64encode(i) {
    if (i == 0) {
        return alphabet.charAt(0);
    } else {
        return b64encode(Math.floor(i / 64)) + alphabet.charAt(i % 64);
    }
}