通过js添加标签之后，点击事件失效了

在我添加标签之前点击事件还是有效果的，但是在我点击添加按钮添加之后点击事件就失效了，在控制台可以用for循环把 lst 数组里每一个的 innerText 打印的出来具体看图

下面是代码


<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="css.css">
</head>

<body>
    <div id="addTo">

        主类 <input type="text" name="" id="mainClass"> 子类 <input type="text" name="" id="subClass">
        <input type="button" id="addJ" value="添加">

    </div>
    <div id="mainbox">
        <div class="box1">
            <p>菜单栏</p>
            <ul>
                <li class="lis">首页</li>
                <li class="lis">客服</li>
                <li class="lis">帮助</li>
            </ul>
        </div>
        <div class="box1">
            <p>工作栏</p>
            <ul>
                <li class="lis">首页1</li>
                <li class="lis">客服1</li>
                <li class="lis">帮助1</li>
            </ul>
        </div>
        <div class="box1">
            <p>展示栏</p>
            <ul>
                <li class="lis">首页2</li>
                <li class="lis">客服2</li>
                <li class="lis">帮助2</li>
            </ul>
        </div>
    </div>



</body>
<script src="js.js"></script>

</html>

var lis = document.getElementsByClassName("lis");
var but1 = document.getElementById("addJ");
var mbox = document.getElementById("mainbox");
var mclass = document.getElementById("mainClass");
var sclass = document.getElementById("subClass");

function getStyle(obj, styleName) {
    if (obj.currentStyle) {
        return obj.currentStyle[styleName];
    } else {
        return getComputedStyle(obj, null)[styleName];
    }
}
but1.onclick = function() {
    if (mclass.value == "" || sclass.value == "") {
        return;
    }
    mbox.style.width = parseInt(getStyle(mbox, "width")) + 187 + "px";
    mbox.innerHTML = mbox.innerHTML + "<div class='box1'><p>" + mclass.value + "</p><ul><li class='lis'>" + sclass.value + "1</li><li class='lis'>" + sclass.value + "2</li><li class='lis'>" + sclass.value + "3</li></ul></div>"
}

for (let i = 0; i < lis.length; i++) { 
    lis[i].onclick = function() {
        console.log("点击了", this.innerText); 
    }
}