计算可输入字数

html代码：

<input maxlength="10" onkeyup="javascript:setShowLength(this, 10, 'cost_title_length');" size="10" type="text" /> <span id="cost_title_length">0/10</span>

js脚本代码：

function setShowLength(obj, maxlength, id) { 
         var rem = maxlength - obj.value.length; 
         var wid = id; 
         if (rem < 0){ 
             rem = 0; 
         }
         document.getElementById(wid).innerHTML =  rem + "/10"; 
    }

setShowLength(document.getElementById("schoolName"),10,"cost_title_length");

参考网址：https://blog.csdn.net/ywj5200/article/details/53380655