Conversion methods between Base64-URL and standard Base64.

base64-convert.js

export function base64url(base64) {
    return String(base64).replace(/[^A-Za-z0-9_-]/g, m =>
        m === '+' ? '-' :
        m === '/' ? '_' :
        ''
    );
}

export function base64standard(base64) {
    base64 = String(base64).replace(/[^A-Za-z0-9+/]/g, m =>
        m === '-' ? '+' :
        m === '_' ? '/' :
        ''
    );
    switch (base64.length % 4) {
        case 1: return base64 + '===';
        case 2: return base64 + '==';
        case 3: return base64 + '=';
        default: return base64;
    }
}