Convert base64 to and from web-safe variant

base64-web-safe.js

// Convert from normal to web-safe, strip trailing "="s
function webSafe64(base64) {
    return base64.replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
}

// Convert from web-safe to normal, add trailing "="s
function normal64(base64) {
    return base64.replace(/\-/g, '+').replace(/_/g, '/') + '=='.substring(0, (3*base64.length)%4);
}