Javascript对网页输入框的字数限制

js对输入框的字数限制，限制文本框输入的字符数,若达到数目则停止其输入!代码如下：

01. !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"
02.html xmlns="http://www.w3.org/1999/xhtml"
03.head
04.meta http-equiv="Content-Type" content="text/html; charset=utf-8" /
05.title无标题文档/title
06.script type="text/javascript"
07.   
var textCounter=function (field,counter,maxlimit){
08.       
var charcnt = field.value.length;
09.       
if (charcnt maxlimit) {
10.           
field.value = field.value.substring(0, maxlimit);
11.       
}else {
12.           
document.getElementById(counter).innerHTML=charcnt;
13.       
}
14.   
}
15./script
16./head
17.body
18.pspan id="progressbar1"0/span/12/p
19.forminput type="text" id="maxcharfield"  size="34"/
20./form
21.script type="text/javascript"
22.   
document.getElementById("maxcharfield").onfocus = document.getElementById("maxcharfield").onkeydown = document.getElementById("maxcharfield").onkeyup = function(){
23.       
textCounter(this,'progressbar1',12);
24.   
}
25./script
26./body
27./html