wvpv/file-upload-cb.html

## file-upload-cb.html
<script runat="server" language="ampscript">

  set @processingPageURL = "https://YOURTENANTHERE.pub.sfmc-content.com/YOURPATHHERE"

</script><!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
    <meta name="viewport" content="width=device-width,initial-scale=1">
    <title></title>
    <style>
      body {
        font-size: 13px;
        font-family: sans-serif;
      }
    </style>

  </head>
  <body>
    Please select a file to upload:
    <br><input id="file" type="file" accept="image/*">
    <br><br><button id="button">Upload</button>
    <div id="responseMessage"></div>

    <script>

      document.getElementById("button")
          .addEventListener("click", function() {
              var files = document.getElementById("file").files;
              if (files.length > 0) {
                  encodeFile(files[0]);
              }
          });

      function encodeFile(file) {

          var reader = new FileReader();
          reader.readAsDataURL(file);

          reader.onload = function() {

              //prepare data to pass to processing page
              var rawImage = reader.result;
              var base64EncodedImage = rawImage.split(";base64,")[1];
              var fullFileName = document.getElementById("file").files[0].name;
              var fileNameRoot = fullFileName.split(".")[0];
              var fileExtension = fullFileName.split(".")[1];

              fetch('%%=v(@processingPageURL)=%%', {
                  method: 'POST',
                  headers: {'Content-type': 'application/json; charset=UTF-8'},
                  body: JSON.stringify({
                          base64EncodedImage: base64EncodedImage,
                          fullFileName: fullFileName,
                          fileNameRoot: fileNameRoot,
                          fileExtension: fileExtension
                  })
              }).then(function (response) {

                  // successful reply
                  if (response.ok) {
                      return response.json();
                  }
                  return Promise.reject(response);

              }).then(function (data) {

                  // successful response
                  console.log(data);
                  responseMessage.innerHTML = "Got it!";

              }).catch(function (error) {

                  // there was a problem
                  console.warn(error);
                  responseMessage.innerHTML = "Oops!";

              });

          };
          reader.onerror = function(error) {
              console.log(error);
          };
      }
    </script>
</body>
</html>
	<script runat="server" language="ampscript">

	set @processingPageURL = "https://YOURTENANTHERE.pub.sfmc-content.com/YOURPATHHERE"

	</script><!DOCTYPE html>
	<html>
	<head>
	<meta charset="UTF-8">
	<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
	<meta name="viewport" content="width=device-width,initial-scale=1">
	<title></title>
	<style>
	body {
	font-size: 13px;
	font-family: sans-serif;
	}
	</style>

	</head>
	<body>
	Please select a file to upload:
	<br><input id="file" type="file" accept="image/*">
	<br><br><button id="button">Upload</button>
	<div id="responseMessage"></div>

	<script>

	document.getElementById("button")
	.addEventListener("click", function() {
	var files = document.getElementById("file").files;
	if (files.length > 0) {
	encodeFile(files[0]);
	}
	});

	function encodeFile(file) {

	var reader = new FileReader();
	reader.readAsDataURL(file);

	reader.onload = function() {

	//prepare data to pass to processing page
	var rawImage = reader.result;
	var base64EncodedImage = rawImage.split(";base64,")[1];
	var fullFileName = document.getElementById("file").files[0].name;
	var fileNameRoot = fullFileName.split(".")[0];
	var fileExtension = fullFileName.split(".")[1];

	fetch('%%=v(@processingPageURL)=%%', {
	method: 'POST',
	headers: {'Content-type': 'application/json; charset=UTF-8'},
	body: JSON.stringify({
	base64EncodedImage: base64EncodedImage,
	fullFileName: fullFileName,
	fileNameRoot: fileNameRoot,
	fileExtension: fileExtension
	})
	}).then(function (response) {

	// successful reply
	if (response.ok) {
	return response.json();
	}
	return Promise.reject(response);

	}).then(function (data) {

	// successful response
	console.log(data);
	responseMessage.innerHTML = "Got it!";

	}).catch(function (error) {

	// there was a problem
	console.warn(error);
	responseMessage.innerHTML = "Oops!";

	});

	};
	reader.onerror = function(error) {
	console.log(error);
	};
	}
	</script>
	</body>
	</html>