console 命令行工具 X clear

console

let tadom = document.getElementsByTagName('textarea')[0];
let span = document.getElementsByTagName('span')[0];
let regExp = /.$/gm;
tadom.addEventListener('input',() => {
    span.innerText = (tadom.value.match(regExp) || [] ).length
})

<textarea></textarea>
<span>0</span>