js判断第几个li

// 获取包含所有<li>元素的<ul>或<ol>
var list = document.getElementById('myList');
var items = list.getElementsByTagName('li');

// 假设我们要找的<li>元素有一个特定的id
var targetItem = document.getElementById('targetLi');

// 将HTMLCollection转换为数组，并找到目标元素的索引
var index = Array.prototype.indexOf.call(items, targetItem);

// 因为数组索引是从0开始的，所以我们需要加1来得到<li>元素在列表中的位置
var position = index + 1;

console.log('The <li> element is at position: ' + position);

var list = document.getElementById('myList');
var items = list.getElementsByTagName('li');
var targetItem = document.getElementById('targetLi');
var position = 1; // 因为是第几个，所以从1开始计数

for (var i = 0; i < items.length; i++) {
    if (items[i] === targetItem) {
        position = i + 1; // 加1是因为计数是从1开始的
        break;
    }
}

console.log('The <li> element is at position: ' + position);

var list = document.getElementById('myList');
var items = Array.from(list.getElementsByTagName('li'));
var targetItem = document.getElementById('targetLi');

var index = items.findIndex(function(item) {
    return item === targetItem;
});

var position = index + 1; // 加1是因为计数是从1开始的

console.log('The <li> element is at position: ' + position);