手机触屏版想要自动弹出键盘要满足的三个条件：
1、文本框获取焦点
2、手触屏该页面的屏幕
3、无延迟
实现实例(类似微信微博):
<!DOCTYPE html>
<html lang="zh-cn">
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<style>
.page{
100%;
height:400px;
background:#333;
overflow:hidden;
}
.page a{
display: block;
50px;
height:50px;
margin:100px auto;
}
.com {
display: none;
100%;
height:500px;
overflow:hidden;
}
.com textarea{
display: block;
90%;
height:200px;
margin:50px auto;
}
</style>
<body>
<div class="page">
<a href="javascript:void(0);">评论</a>
</div>
<div class="com">
<textarea></textarea>
</div>
</body>
<script>
$('.page a').on('click',function(){
$('.page').hide()
$('.com').show()
$('.com textarea').focus()
})
</script>
</html>