【每日一题】– 2019-09-11 - 实现querySelector about fe-interview HOT 1 CLOSED

function matchSelector(selector, element) {
  if (Array.prototype.includes.call(element.classList, selector.slice(1))) return true;
  return false;
}
function querySelector(selector, element) {
  if (element === null) return null;
  const children = element.children;
  let res = null;
  for(let child of children) {
    if (matchSelector(selector, child)) return child;
    res = querySelector(selector, child);
    if (res !== null) return res;
  }
  return null;
}

querySelector('.test', document.body);