js的onfocus,onblur事件

<!DOCTYPE html>
<html>
<head>
    <title></title>
</head>
<body>
    <label for="txt">姓名：</label>
    <input >
    <span ></span>
</body>
<script type="text/javascript">
    var txt=document.getElementById("txt");
    txt.onfocus=function(){
        //友好提示
        var span=document.getElementById("action");
        span.innerHTML="用户格式最小8位";
        span.style.color="#0f0";
    };
    txt.onblur=function(){
        var span=document.getElementById("action");
        span.innerHTML="对不起，格式不正确";
        span.style.color="#f00";
    }
</script>
</html>

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