<ul id="oul">

    <li>1</li>

    <li>2</li>

    <li>3</li>

    <li>4</li>

    <li>5</li>

</ul>

<button id="btn">添加元素</button>

let oUl = document.getElementById('oul')

let lis = oUl.getElementsByTagName('li')

let btn = document.getElementById('btn')

btn.onclick = function(){

    let oLi = document.createElement('li');

    oLi.innerHTML = lis.length+1

    oUl.appendChild(oLi)

}

oUl.onclick = function(event) {

    var e = event || window.event;

    console.log(e.target.innerHTML)

}

oUl.onclick = function(event) {

    var e = event || window.event;

    // 判断点击的元素是不是代理元素

    if(e.target == this){

        return

    }

    console.log(e.target.innerHTML)

}