27.事件委托

// 循环创建10个li标签，当点击li标签时，打印其对应的索引
<ul id="list"></ul>
function loadNode(len) {
  var html = '';
  for (let index = 0; index < 10; index++) {
    html += '<li>'+index+'</li>';
  }
  var list = document.getElementById('list');
  list.onclick = function(event) {
    event = event || window.event;
    var target = event.target || event.srcElement;
    if(target.nodeName.toLowerCase() === 'li') {
      console.log(target.innerText);
    }
  }
  list.innerHTML = html;
}
loadNode();