Automação: Redimensiona imagem e depois deixa baixar

<!DOCTYPE html>
<html>
  <head>
    <script>
      function uploadImage(input) {
        var reader = new FileReader();
        reader.onload = function (event) {
          var image = new Image();
          image.onload = function () {
            var width = parseInt(prompt("Informe a largura desejada:", "1280"));
            var height = parseInt(prompt("Informe a altura desejada:", "720"));
            var canvas = document.createElement("canvas");
            canvas.width = width;
            canvas.height = height;
            var ctx = canvas.getContext("2d");
            ctx.drawImage(image, 0, 0, width, height);
            document.getElementById("image").src = canvas.toDataURL();
            document.getElementById("downloadButton").style.display = "block";
            document.getElementById("image").style.display = "block";
          };
          image.src = event.target.result;
        };
        reader.readAsDataURL(input.files[0]);
      }

      function downloadImage() {
        var d = new Date();
        var dateString = d.getDate() + "-" + (d.getMonth() + 1) + "-" + d.getFullYear();
        var timeString = d.getHours() + "-" + d.getMinutes() + "-" + d.getSeconds();
        var image = document.getElementById("image");
        var link = document.createElement("a");
        link.download = dateString + "-" + timeString + "-resized-image.png";
        link.href = image.src;
        link.click();
      }
    </script>
  </head>
  <body>
    <input type="file" onchange="uploadImage(this)">
    <br><br>
    <img id="image" src="" style="display: none">
    <br><br>
    <button id="downloadButton" onclick="downloadImage()" style="display: none">Baixar imagem</button>
  </body>
</html>