输入剩余字数

function checkLen2(obj)  
{ 
   var maxChars = 200;//最多字符数 
   if (obj.value.length > maxChars) 
   obj.value = obj.value.substring(0,maxChars); 
   var curr = maxChars - obj.value.length; 
   document.getElementById("count2").innerHTML = curr.toString(); 
}