Encode and Decode Messages

function encodeAndDecodeMessages() {
    let textarea = document.getElementsByTagName('textarea');
    [...document.getElementsByTagName('button')].forEach(b => b.addEventListener('click', message));

    function message(btn) {
        if (btn.target.textContent === 'Encode and send it') {
            let encoded = [...textarea[0].value].map(e => String.fromCharCode(e.charCodeAt(0) + 1)).join('');
            textarea[1].value = encoded;
            textarea[0].value = '';
        } else if (btn.target.textContent === 'Decode and read it') {
            let decoded = [...textarea[1].value].map(e => String.fromCharCode(e.charCodeAt(0) - 1)).join('');
            textarea[1].value = decoded;
        }
    }
}