<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel='stylesheet prefetch' href='https://res.wx.qq.com/open/libs/weui/0.3.0/weui.css'>
</head>
<body>
<div class="weui_cells_title">意见反馈</div>
<div class="weui_cells weui_cells_form">
<div class="weui_cell_bd weui_cell_primary">
<textarea class="weui_textarea" id="textarea" placeholder="请输入意见反馈" rows="3"></textarea>
<div class="weui_textarea_counter"><span id="count">0</span>/200</div>
</div>
</div>
<script src="//cdn.bootcss.com/jquery/3.1.0/jquery.min.js"></script>
<script>
$(function(){
var max = 200;
$('#textarea').on('input', function(){
var text = $(this).val();
var len = text.length;
$('#count').text(len);
if(len > max){
$(this).closest('.weui_cell').addClass('weui_cell_warn');
}
else{
$(this).closest('.weui_cell').removeClass('weui_cell_warn');
}
});
})
</script>
</body>
</html>
完整方案,需要引用jquery。