let lis = document.getElementsByTagName('li');

for (let i = 0; i < lis.length; i++) {

//    备份文字

let result = lis[i].innerHTML;

// console.log(result);

lis[i].addEventListener('mouseenter', function () {

lis[i].style.color = 'red';

lis[i].style.fontSize = '35px';

lis[i].innerHTML = lis[i].innerHTML + '我是第' + (i + 1) + '个'

}, false);

lis[i].addEventListener('mouseleave', function () {

lis[i].style.color = 'black';

lis[i].style.fontSize = '16px';

lis[i].innerHTML = result;

}, false)

}