javascript ,jq 实现input随文字变化而变化

<input name="text" onkeyup="checkLength(this)"/>

<script language="javascript">        function checkLength(which) {           var  iCount = which.value.replace(/[^\u0000-\u00ff]/g,"aa").length;               which.size=iCount+2;        }</script>

        var textWidth = function(text){            var sensor = $('<pre>'+ text +'</pre>').css({display: 'none'});            $('body').append(sensor);            var width = sensor.width();            sensor.remove();            return width;        };        $("input").unbind('keyup').bind('keyup', function(){            $(this).width(textWidth($(this).val()+20));        });