js 限制输入字数 （ 包括粘贴 ）

<input name="title" type="text" size="50" value="" maxlength="15" onkeyup="javascript:setShowLength(this, 15, 'cost_tpl_title_length');"onpaste="javascript:setShowLength(this, 15, 'cost_tpl_title_length');"><span class="red" id="cost_tpl_title_length">还可以输入15字数</span> 

function setShowLength(obj, maxlength, id) { 

 setTimeout(function(){

var rem = maxlength - obj.value.length; 
var wid = id; 
if (rem < 0){ 
rem = 0; 
} 

document.getElementById(wid).innerHTML = "还可以输入" + rem + "字数"; 

},100);

}