Javascript 当文件上载控件上没有任何文件时显示消息单击按钮

我的页面上有一个文件上载控件，我想限制只接受.csv文件，并在试图上载任何其他文件时抛出消息。此外，当没有选择任何文件并且单击了上载按钮时，它应该抛出消息

Html-

<div class="panel panel-primary">
    <div class="panel-heading">00</div>
    <div class="panel-body">
        <div class="field_row">
            <input type="file" accept=".csv" id="fileUpload" name="fileUpload1" />
        </div>
        <br />
        <div class="field_row">
            <div class="col-lg-12">
                <div class="form-group">
                    <center><div class="col-lg-3"><div class="input-append" id="filterDev" style="visibility: hidden">
                        <input name="search" id="inputFilter" placeholder="Enter ID to filter" />
                        <input type="button" value="Filter" id="filter" class="btn btn-primary" />
                    </div></div></center>
                    <div class="col-lg-6"></div>
                    <input type="button" id="upload" value="Upload" class="btn btn-primary" />
                    <input type="button" id="cancel" value="Cancel/Save" style="visibility: hidden" class="btn btn-primary" />
                    <input type="button" id="process" value="Process" style="visibility: hidden" class="btn btn-primary" />
                </div>
            </div>

            <div class="row">
                <div class="col-lg-12">
                    <div class="panel panel-default" style="align-self: center">
                        <div class="panel-body" style=" max-height:600px; min-height: 400px; overflow-y: scroll;">

                            <div class="row">
                                <div class="col-sm-12" id="dvCSV">
                                    <table id="my-table">
                                    </table>
                                </div>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
        </div>

        <div class="row">
            <div class="col-sm-12">
                <p id="download" style="color: cornflowerblue; visibility: hidden"><strong>Please click the below links to download the processed file..</strong></p>
            </div>
        </div>
        <div class="row">
            <div class="col-sm-12">
                <div class="col-sm-3">
                    <p id="File1" style="color: cornflowerblue; text-decoration: underline; visibility: hidden"><a href="Files/CommitteeMembers.xlsx">File1 Download</a></p>
                </div>
                <div class="col-sm-3">
                    <p id="File2" style="color: cornflowerblue; text-decoration: underline; visibility: hidden"><a href="Files/GSD_Offering_Completion.csv">File2 Download</a></p>
                </div>
            </div>
        </div>
    </div>
</div>
</div>

<script type="text/javascript">

    $("#cancel").on("click", function () {
        $('input:checked').each(function () {
            $(this).closest("tr").remove();
        });
    });


    $(function () {
        $("#process").bind("click", function () {

            document.getElementById("File1").style.visibility = "visible";
            document.getElementById("File2").style.visibility = "visible";
            document.getElementById("download").style.visibility = "visible";

        });

    });

    $("#filter").click(function () {
        ids = $("#inputFilter").val();
        if (ids != "") {
            idsArray = ids.split(",");
            $("#my-table tr:gt(0)").hide();
            $.each(idsArray, function (i, v) {
                $("#my-table tr[data-id=" + v + "]").show();
            })
        } else {
            $("#my-table tr").show();
        }
    });


    /*  $("#File1").click(function () {
          window.location = "Files/CommitteeMembers.xlsx";
      });
      $("#File1").click(function () {
          window.location = "Files/GSD_Offering_Completion.xlsx";
      });*/

</script>

00


请单击以下链接下载处理后的文件。


$（“#取消”）。在（“单击”上，函数（）{
$（'input:checked'）。每个（函数（）{
$（this）.tr.remove（）；
});
});
$（函数（）{
$（“#进程”）.bind（“单击”，函数（）{
document.getElementById（“File1”）.style.visibility=“可见”；
document.getElementById（“File2”）.style.visibility=“可见”；
document.getElementById（“下载”）.style.visibility=“可见”；
});
});
$（“#过滤器”）。单击（函数（）{
ids=$（“#inputFilter”）.val（）；
如果（ID！=“”）{
idsArray=ids.split（“，”）；
$（“#我的表tr:gt（0）”）.hide（）；
$.each（数组、函数（i、v）{
$（“#我的表tr[data id=“+v+”]）。show（）；
})
}否则{
$（“#我的桌子tr”）.show（）；
}
});
/*$（“#文件1”）。单击（函数（）{
window.location=“Files/committeembers.xlsx”；
});
$（“#文件1”）。单击（函数（）{
window.location=“Files/GSD\u Offering\u Completion.xlsx”；
});*/

Javascript-

$(function () {
    $("#upload").bind("click", function () {
        var regex = /^([a-zA-Z0-9\s_\\.\-:])+(.csv|.txt)$/;

        if (regex.test($("#fileUpload").val().toLowerCase())) {
            if (typeof (FileReader) != "undefined") {
                var reader = new FileReader();
                reader.onload = function (e) {
                    //var table = $("<table id='name'/>");
                    var lines = e.target.result.split("\n");
                    //alert(lines);
                    var result = [];


                    var headers = lines[0].split(",");
                    for (var i = 1; i < headers.length; i++) {
                        var header = headers[i];
                        header = header.replace(/(\r\n|\n|\r)/gm, "");
                        headers[i] = header;
                    }



                    for (var i = 1; i < lines.length; i++) {
                        var obj = {};
                        var currentline = lines[i].split(",");
                        //alert(currentline);

                        for (var j = 0; j < headers.length; j++) {
                            obj[headers[j]] = currentline[j];
                            //alert(obj[headers[j]]);
                        }
                        result.push(obj);
                        //alert(JSON.stringify(result));
                    }

                    //alert(result[0].NAME + ' '+ result[0].ADDRESS+" "+result[0].CITY);
                    populateTable(result);
                    document.getElementById("cancel").style.visibility = "visible";
                    document.getElementById("process").style.visibility = "visible";
                    document.getElementById("filterDev").style.visibility = "visible";
                }
                reader.readAsText($("#fileUpload")[0].files[0]);
            }

        }

    });
});

$(function () {
    $("#process").bind("click", function () {

        document.getElementById("File1").style.visibility = "visible";
        document.getElementById("File2").style.visibility = "visible";

    });

});

function populateTable(finalObject) {

    var obj = finalObject;
    var table = $("<table id='my-table' />");
    table[0].border = "1";
    var columns = Object.keys(obj[0]);
    columns.unshift('');
    //alert(columns);
    var columnCount = columns.length;
    var row = $(table[0].insertRow(-1));


    for (var i = 0; i < columnCount; i++) {
        var headerCell = $("<th />");
        headerCell.html([columns[i]]);
        row.append(headerCell);
    }

    $.each(obj, function (i, obj) {

        row = '<tr data-id="' + obj.ID + '"><td><input type="checkbox"/></td><


    var dvTable = $("#dvCSV");
    dvTable.html("");
    dvTable.append(table);

} 

$（函数（）{
$（“#上载”）.bind（“单击”），函数（）{
var regex=/^（[a-zA-Z0-9\s\\\.\-：]）+（.csv|.txt）$/；
if（regex.test（$（“#fileUpload”）.val（）.toLowerCase（））{
if（typeof（FileReader）！=“未定义”）{
var reader=new FileReader（）；
reader.onload=函数（e）{
//变量表=$（“”）；
变量行=e.target.result.split（“\n”）；
//警戒线；
var结果=[]；
var headers=行[0]。拆分（“”，“”）；
对于（变量i=1；i

如何实现这一点