js判断还能输入字符

51漂泊

<h3>51漂泊网（200字以内）</h3>
<textarea onkeyup="checkLen(this)"></textarea>
<div>您还可以输入 <span id="count">200</span> 个文字</div>
  
<script type="text/javascript">
function checkLen(obj)  
{
    var maxChars = 200;//最多字符数
    if (obj.value.length > maxChars)
    obj.value = obj.value.substring(0,maxChars);
    var curr = maxChars - obj.value.length;
    document.getElementById("count").innerHTML = curr.toString();
}
</script>