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javascript - when i am updating my list then its not getting updated in the backend the count of list is still the same why?

问题描述

I am trying to update a list, but when I add a new element and then count the no. of the element in that list it is still the same as the previous value

here is the code

I am trying to update the section name in the file by clicking on the list its working fine when I don't add any new section, but as I add a new section the eventListener on li stop working.


<!DOCTYPE html>
<html>
<head>
    <title>sections</title>
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/css/bootstrap.min.css" integrity="sha384-9aIt2nRpC12Uk9gS9baDl411NQApFmC26EwAOH8WgZl5MYYxFfc+NcPb1dKGj7Sk" crossorigin="anonymous">
    <link rel="stylesheet" type="text/css" href="styles.css">


</head>
<body>

    <div class="container-fluid">
      <div class="row">
        <div class="sidebar col col-lg-3">
            <center><h3>Sections</h3></center><hr>
            <ul class="list">

            <li>K19SP</li>
            <hr>
            <li>K19PV</li>
            <hr>
            <li>K19MA</li>
            <hr>
            <li>K19RQ</li>
            <hr>
            <li>K19MS</li>
            <hr>
            <li>K19LS</li>
            <hr >
            <li>K19DQ</li>
            <hr>
            <li>K19MR</li>
            <hr>
            <li>K19OH</li>
            <hr>
        </ul>
        </div>
        <div class="col col-lg-9">
            <center><h3 id='head'></h3></center>
            <div class="sidebar-right col col-lg-3">
             <button class="btns">Add Student</button>
             <button class="btns">Remove Student</button>
             <button class="btns">Upload Assignment</button>
             <button class="btns">View Status</button>
             <button class="btns"> Upload Reading Material</button>
             <button class="btns">Remove Section</button>
            </div>
        </div>
       </div>
       <div class="row">
        <div class="col col-lg-3">

            <input type="text" name="sect" id="sect">
            <button type="button" id="add" onclick="getInput()">ADD</button>

        </div>
       </div>
    </div>

<script type="text/javascript" src="app.js">

</script>
<script src="https://code.jquery.com/jquery-3.5.1.slim.min.js" integrity="sha384-DfXdz2htPH0lsSSs5nCTpuj/zy4C+OGpamoFVy38MVBnE+IbbVYUew+OrCXaRkfj" crossorigin="anonymous"></script>
<script src="https://cdn.jsdelivr.net/npm/popper.js@1.16.0/dist/umd/popper.min.js" integrity="sha384-Q6E9RHvbIyZFJoft+2mJbHaEWldlvI9IOYy5n3zV9zzTtmI3UksdQRVvoxMfooAo" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/js/bootstrap.min.js" integrity="sha384-OgVRvuATP1z7JjHLkuOU7Xw704+h835Lr+6QL9UvYjZE3Ipu6Tp75j7Bh/kR0JKI" crossorigin="anonymous"></script>
</body>
</html>


this is javascript


 var ul = document.querySelector('ul');
    var input = document.getElementById('sect');
    var head = document.querySelector('#head');

function getInput() {
ul.innerHTML = ul.innerHTML + "<li>"+input.value+"</li> <hr>";
}

var li = document.querySelectorAll('li');
var total = document.querySelectorAll('li').length;

for(let i=0 ; i< total ; i++)
{
    li[i].addEventListener('click',() => {  head.innerHTML = li[i].innerHTML});
}

标签： javascripthtml

解决方案

Replace your script with below code. Each time you add a new item , you need add the listener to that li. UpdateListener() will do that for you.

<script>
  var ul = document.querySelector('ul');
  var input = document.getElementById('sect');
  var head = document.querySelector('#head');

function getInput() {
    ul.innerHTML = ul.innerHTML + "<li>"+input.value+"</li> <hr>";
    UpdateListener();
}

function UpdateListener(){
    var li = document.querySelectorAll('li');
    var total = document.querySelectorAll('li').length;

 for(let i=0 ; i< total ; i++)
 {
    li[i].addEventListener('click',() => {  

    head.innerHTML = li[i].innerHTML

    });
 }
}

  UpdateListener();

</script>

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