一、实现效果：
二、代码
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>微博字数统计</title>
<style type="text/css">
.content{
width: 400px;
height: 300px;
border: 1px solid red;
}
textarea{
width: 350px;
height: 100px;
margin-left: 10px;
}
</style>
</head>
<body>
<div class="content">
<form action="#" method="post">
<p class="shuru">你还可以输入<font color="#FF0000"><span></span></font>个字符。</p>
<label>
<textarea></textarea>
</label>
</form>
</div>
<script src="js/jquery-1.11.1.min.js" charset="UTF-8" type="text/javascript"></script>
<script type="text/javascript">
$(function(){
var text=$(".content textarea").val();
var counter=text.length;
$(".shuru span").text(100-counter);
$(document).keyup(function(){
var text=$(".content textarea").val();
var counter=text.length;
if(counter>=100){
$(".shuru span").text("对不起，您输入的字数太长了！");
$(".content textarea").attr("readonly",true);
}else{
$(".shuru span").text(100-counter);
}
})
})
</script>
</body>
</html>
ok
