计算可输入字数

<textarea id="content" maxlength="50" onkeyup="javascript:setShowLength(this,50,'count_length')"></textarea>

<div id="count_length">您还可以输入50个字</div>

<script>

	function setShowLength(obj,maxlength,id){

	    var rem = maxlength - obj.value.length;

	    var _id = id;

	    if(rem < 0){

		rem = 0;

            }

	    document.getElementById(_id).innerHTML = "您还可以输入" + rem +"个字";

	}

        //兼容ie字数限制

       $("#content").on("textarea propertychange",function(){

           var $this = $(this),

	        _val = $this.val();

            if(_val.length > 50){

		$this.val(_val.substring(0,50));

            }

       });

</script>