判斷日期,輸出成YYYY/MM/DD形式

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<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>轉換日期</title>
<script type="text/javascript">
String.prototype.IsDate=function(){
    var dateReg=/^[1-3]\d{3}(\/|-)?((1[0-2])|(0?[1-9]))(\/|-)?((0?[1-9])|([1-2]\d)|(3[01]))$/;
    var rdelimiter="/";
    var nDate;
    if(dateReg.test(this)){
        var iDate=this.replace(/\//g,"").replace(/-/,"");
        if(iDate.length == 6){
            nDate = iDate.substr(0, 4)+rdelimiter+"0"+iDate.substr(4, 1)+rdelimiter+"0"+iDate.substr(5, 1);
        }else{
            var nMonth = parseInt(iDate.substr(4, 2));
            if(nMonth > 12){    //月份為一位
                nDate = iDate.substr(0, 4)+rdelimiter+"0"+iDate.substr(4, 1)+rdelimiter+iDate.substr(5, 2);
            }else{
                var nDay = "0"+iDate.substr(6, 2);
                nDate = iDate.substr(0, 4)+rdelimiter+"0"+iDate.substr(4, 2)+rdelimiter+"0"+nDay.substr(nDay.length-2, 2);
            }
        }
        if(isNaN(new Date(nDate))){
            return false;
        }else{
            return true;
        }
    }else{
        return false;
    }
}
/**//*********************************************************
**    名稱：getFormatDate()                                **
**  功能：格式化日期                                    **
**    參數: iDate        ：轉換前日期YYYY-M/D或YYYY/MM/DD    **
**         idelimiter    ：轉換前日期分格符                    **
**         rdelimiter    ：轉換後的分格符,默認為"/"            **
**    返回: String,YYYY+分格符+MM+分格符+DD                **
*********************************************************/
function getFormatDate(iDate, idelimiter, rdelimiter){
    var regStr;
    var delimiter;
    var tDate;
    var rDate;
    var rMonth;
    var rDay;
    if(rdelimiter == ""){
        rdelimiter="/";
    }
    //替換掉分隔符
    for(var i=0; i<idelimiter.length; i++){
        delimiter=idelimiter.substr(i, 1);
        if(delimiter == "/"){
            iDate=iDate.replace(/\//g, "");
        }else{
            regStr = "iDate=iDate.replace(/"+delimiter+"/g, '');";
            eval(regStr);
        }
    }
    if(iDate.length == 6){
        nDate = iDate.substr(0, 4)+rdelimiter+"0"+iDate.substr(4, 1)+rdelimiter+"0"+iDate.substr(5, 1);
    }else{
        var nMonth = parseInt(iDate.substr(4, 2));
        if(nMonth > 12){    //月份為一位
            nDate = iDate.substr(0, 4)+rdelimiter+"0"+iDate.substr(4, 1)+rdelimiter+iDate.substr(5, 2);
        }else{
            var nDay = "0"+iDate.substr(6, 2);
            nDate = iDate.substr(0, 4)+rdelimiter+"0"+iDate.substr(4, 2)+rdelimiter+"0"+nDay.substr(nDay.length-2, 2);
        }
    }

    tDate=new Date(nDate);
    if(isNaN(tDate)){
        throw("日期非法");
    }
    rMonth = "00"+(tDate.getMonth()+1).toString();
    rMonth = rMonth.substr(rMonth.length-2, 2);
    rDay = "00"+tDate.getDate().toString();
    rDay = rDay.substr(rDay.length-2, 2);
    rDate = tDate.getFullYear().toString() + rdelimiter + rMonth + rdelimiter + rDay;
    return rDate;
}
function test(){
    var cText=document.getElementById("test");
    if(cText.value.IsDate()){
        cText.value=getFormatDate(cText.value, "/-", "/");
        return true;
    }else{
        alert("日期格式不正確或非法,正確輸入格式是YYYY/MM/DD或YYYYMMDD");
        return false;
    }
}
</script>
</head>

<body>
<input type="text" id="test" />
<input type="button" value="測試" onclick="test()" />
</body>
</html>

原文地址：https://www.cnblogs.com/ywkpl/p/1325553.html