fiddle/public/js/console-panel.js

const output = () => document.getElementById('console-output');

export function initConsole() {
  window.addEventListener('message', (e) => {
    if (!e.data || e.data.type !== 'console') return;
    if (e.data.method === 'clear') {
      clearConsole();
      return;
    }
    appendLine(e.data.method, (e.data.args || []).join(' '));
  });

  document.getElementById('btn-clear-console').addEventListener('click', clearConsole);
}

function appendLine(method, text) {
  const el = document.createElement('div');
  el.className = `console-line console-${method}`;
  el.textContent = text;
  const out = output();
  out.appendChild(el);
  out.scrollTop = out.scrollHeight;
}

export function clearConsole() {
  output().innerHTML = '';
}