JavaScript中统计Textarea字数并提示还能输入的字符

<span style="font-size:18px;"><script language="javascript">

function countChar(textareaName,spanName)

{

document.getElementById(spanName).innerHTML = 140 - document.getElementById(textareaName).value.length;

}

</script>

可以输入<span id="counter">140</span>字<br/>

<textarea id="status" name="status" rows="6" cols="40" onkeydown='countChar("status","counter");'

onkeyup='countChar("status","counter");'></textarea></span>