<script type="text/javascript">
$(function(){
$("#iptcont").bind("keydown",function(e){
var key
= e.which,that = this,h = 20;
if (key == 13) {
var brs =
$(this).val().split("\n").length+1;
$(this).attr("rows",brs).height(h*brs);
}else
if(key == 8){
window.setTimeout(function(){
var brs = $(that).val().split("\n").length;
$(that).attr("rows",brs).height(h*brs);
},100);
}
});
});
</script>
<body>
<textarea id="iptcont"
rows="1" style="border:none;height:20px;border-bottom:1px solid
blue;width:200px;resize:none;font-size:18px;line-height:20px;overflow:hidden;"></textarea>
</body>
原文：http://www.cnblogs.com/leejersey/p/3665428.html