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="40" />