html

<div class="rowDriver">
<textarea onkeydown="countChar()" onkeyup="countChar()" rows="10" id="describe" name="describe"
class="textarea" placeholder="请填写随手拍内容" maxlength="200"></textarea>
<span class="rowDriverSpan" id="rowDriverSpan">0/200</span>
</div>

js

function countChar() {
var wordnum = document.getElementById("describe").value.length
if (wordnum >= 201) {
document.getElementById("describe").value = document.getElementById("describe").value.substring(0, 199
)
} else {
//rowDriverSpan这个是span标签的id
rowDriverSpan.innerHTML = wordnum+"/200"
}
}

效果图

image.png