下载时为图像设置唯一名称

Question

我想知道如何才能完成这项工作。我有一个md5代码生成器，所以它可以为每个下载的图像提供唯一的名称但它似乎无法工作。

<script>
$(document).ready(function(){


var element = $("#firstshirt"); // global variable
var getCanvas; // global variable

    $("#btn-Preview-Image").on('click', function () {
         html2canvas(element, {
         onrendered: function (canvas) {
                $("#previewImage").append(canvas);
                getCanvas = canvas;
             }
         });
    });

    $("#btn-Convert-Html2Image").on('click', function () {
    var imgageData = getCanvas.toDataURL("image/png");
    // Now browser starts downloading it instead of just showing it
    var newData = imgageData.replace(/^torcdesign.com:image\/png/, "data:application/octet-stream");
    $("#btn-Convert-Html2Image").attr("download", "$confirm_coded").attr("href", newData);
    });

});

</script>

 <?PHP
$confirm_coded=md5(uniqid(rand())); ?>