<style type="text/css">

.progress{
width: 1px;
height: 14px;
color: white;
font-size: 12px;
overflow: hidden;
background-color: navy;
padding-left: 5px;
}

</style>

<script type="text/JavaScript">

function textCounter(field,counter,maxlimit,linecounter) {
// text width//
var fieldWidth = parseInt(field.offsetWidth);//parseInt 方法 返回由字符串转换得到的整数。将字符串转换成整型。
//obj.offsetWidth 指 obj 控件自身的绝对宽度，不包括因 overflow 而未显示的部分，也就是其实际占据的宽度，整型，单位像素
var charcnt = field.value.length

// trim the extra text
if (charcnt > maxlimit) {
field.value = field.value.substring(0, maxlimit);
}

else {
// progress bar percentage
var percentage = parseInt(100 - (( maxlimit - charcnt) * 100)/maxlimit) ;
document.getElementById(counter).style.width = parseInt((fieldWidth*percentage)/100)+"px";
document.getElementById(counter).innerHTML="已输: "+percentage+"%"
// color correction on style from CCFFF -> CC0000
setcolor(document.getElementById(counter),percentage,"background-color");
}
}

function setcolor(obj,percentage,prop){
obj.style[prop] = "rgb(80%,"+(100-percentage)+"%,"+(100-percentage)+"%)";
}

</script>

<p>限制：120字节</P>
<form>

<textarea rows="5" cols="40" name="maxcharfield" id="maxcharfield"
onKeyDown="textCounter(this,'progressbar1',120)"
onKeyUp="textCounter(this,'progressbar1',120)"
onFocus="textCounter(this,'progressbar1',120)" ></textarea><br />

<div id="progressbar1" class="progress"></div>

<script>textCounter(document.getElementById("maxcharfield"),"progressbar1",120)</script>

</form>