入力可能な文字数メッセージを動的に表示します。また入力可能な文字数

 
<input name="title" type="text" size="50" value="{$p.title}" maxlength="15" onkeyup="javascript:setShowLength(this, 15, 'cost_tpl_title_length');"><span class="red" id="cost_tpl_title_length">     15  </span> 

 
function setShowLength(obj, maxlength, id) 
{ 
var rem = maxlength - obj.value.length; 
var wid = id; 
if (rem < 0){ 
rem = 0; 
} 
document.getElementById(wid).innerHTML = "     " + rem + "  "; 
}