样式

<style>.itp {width: 200px;height: 60px;border: 5px solid red;text-align: center;line-height: 60px;font-size: 30px;margin: 10px;}button {width: 80px;height: 30px;color: rgb(229, 225, 232);border-radius: 4px;font-size: 20px;outline: none;border: none;background-color: blueviolet;/* margin-top: 10px; */}</style>

html

 <div><div class="itp">a</div><button class="ks">开始</button><button class="tz">停止</button><div>你的选择是：<span></span></div></div>

js

  <script>const arr = ['Q', 'W', 'E', 'R', 'T', 'Y', 'U', 'I', 'O', 'P', 'A', 'S', 'D', 'F', 'G', 'H', 'J', 'K', 'L', 'Z', 'X', 'C', 'V', 'B', 'N', 'M']const ks = document.querySelector('.ks')const tz = document.querySelector('.tz')const span= document.querySelector('span')const ipt = document.querySelector('.itp')//  console.log(arr[ran])let iks.addEventListener('click', function () {i= setInterval(function () {let ran = Math.floor(Math.random() * 26)ipt.innerHTML = arr[ran]}, 100)})tz.addEventListener('click',function(){clearInterval(i)span.innerHTML=ipt.innerHTML})</script>

效果：