Which element does javascript get?

<div>
    <li class="img">1</li>
    <li class="img">2</li>
    <li class="img hover">3</li>
    <li class="img">4</li>
    <li class="img">5</li>
</div>

<span>3</span>

above your code hover will be automatically changed in 5 li. How can you rely on js to know which li is currently being hover without refreshing the page?

I thought of an idea, but I haven"t run it yet. In the test, I
first get how many li, there are. Then if the value of hover, in IndexOf.li is greater than 1, find out the subscript of li greater than 1
.
Javascript
Mar.24,2021

after you get the element, you can know how many child elements it is through the parent element of the current element.
template 

<ul>
  <li class="img">1</li>
  <li class="img">2</li>
  <li class="img hover">3</li>
  <li class="img">4</li>
  <li class="img">5</li>
</ul>
<button onclick="getHoverIndex()"></button>

script 

function getHoverIndex() {
  var el = document.querySelector('.hover');
  var index = [].indexOf.call(el.parentElement.children, el);
  console.log(index)
}

event delegate to determine the value of the current clicked object e.target . Or you can bind an identifier attribute to the tag, class or attribute . I think so much for the time being. li is it appropriate to put it in ul ? 

<!DOCTYPE HTML>
<html>
<head>
    <meta charset="utf-8">
    <title>- LI </title>
    <style>
    </style>
</head>
<body>
<ul>
    <li class="img">1</li>
    <li class="img">2</li>
    <li class="img">3</li>
    <li class="img">4</li>
    <li class="img">5</li>
</ul>
<script>
    var nodeList = document.getElementsByTagName('li');
    for (var i = 0; i < nodeList.length; iPP) {
        (function (j) {
            nodeList[j].addEventListener("click", function (e) {
                alert(j)
            }, false);
        })(i);
    }
</script>
</body>
</html>

binding this when distributing events can be solved either by self-calling function using closure or by using es6 syntax let

Previous: A program, always paragraph error, hope you can help me to see where there is a problem?

Next: How do I change the files installed by node modules to the project directory in the vue project?

css mysql arrays josn react html typescript webpack npm sass R objective-c .net sql-server jquery python-3.x angularjs django angular excel regex iphone ajax linux xml pandas vba spring database wordpress string wpf xcode windows bash postgresql oracle multithreading eclipse list firebase algorithm macos forms image scala visual-studio azure bootstrap spring-boot react-native python-2.7 docker performance function winforms matlab powershell apache dataframe api sqlite numpy rest shell selenium flutter dart maven loops qt swing android-studio csv express file class tensorflow sorting codeigniter perl
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1e4c161-44e9b.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1e4c161-44e9b.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
Need Help?