Uint8Array from ArrayBuffer is empty

Question

I have been attempting to write a program that processes files, and to do so I need to convert the array buffer of the file to a Uint8Array. The problem is when I run my code the array is empty. The array I am looking for is the fdata array. PLEASE DO NOT TELL ME TO USE A SERVER SIDE PROGRAM AS I AM UNABLE TO PUT SERVER SIDE CODE ON THE PLATFORM I AM USING.

<body>
  <input type="file" id="files" name="files[]" multiple />
  <div id="outimg"></div>
  <script>
    function handleFileSelect(evt) {
      var files = evt.target.files;
      console.log(files);
      for (var i = 0, f; f = files[i]; i++) {
        var reader = new FileReader();

        reader.onload = (function(theFile) {
          return function(e) {
            console.log(e.target.result);
          };
        })(f);

        reader.readAsArrayBuffer(f);

        fdata = new Uint8Array(reader.result);

        console.log(fdata);

        window.cvd = [];

        for (var i = 0, n = window.fdata.length; i < n; i += 3) {
          var a = Array.from(window.fdata.slice(i, i + 3));
          a.push(255);
          window.cvd.push(a);
        }


      }
    }

    document.getElementById('files').addEventListener('change', handleFileSelect, false);
  </script>
</body>

score 0 · Accepted Answer · answered Dec 19 '18 at 03:07

Reader result is available when the file is loaded so try to access it within the onload event handler:

<body>
  <input type="file" id="files" name="files[]" multiple />
  <div id="outimg"></div>
  <script>
    function handleFileSelect(evt) {
      var files = evt.target.files;
      console.log(files);
      for (var i = 0, f; f = files[i]; i++) {
        var reader = new FileReader();

        reader.onload = (function(theFile) {
          return function(e) {
            console.log(e.target.result);
            fdata = new Uint8Array(reader.result);

            console.log(fdata);

            window.cvd = [];

            for (var i = 0, n = window.fdata.length; i < n; i += 3) {
              var a = Array.from(window.fdata.slice(i, i + 3));
              a.push(255);
              window.cvd.push(a);
            }
          };
        })(f);

        reader.readAsArrayBuffer(f);




      }
    }

    document.getElementById('files').addEventListener('change', handleFileSelect, false);
  </script>
</body>

Uint8Array from ArrayBuffer is empty

1 Answers1