js搜索输入关键词

function getInput(val,a){
    var id = 'ser-key';
    if(a=='focus'){
        document.getElementById(id).value='';
    }
    if(a=='blur'){
        if(val==''){
            document.getElementById(id).value= "请输入VIP卡号或手机号码查询";
        }else{
            document.getElementById(id).value= val;
        }

    }
}

 <input name="keyword" type="text" class="inp_a" id="ser-key" onfocus="getInput(this.value,'focus')" onblur="getInput(this.value,'blur')" value="请输入VIP卡号或手机号码查询" size="" />