<input type="file" onchange="fileChange(this)">

<script>
  async function fileChange(f) {

    //TODO: check if file is jpeg.

    let base64 = await this.convertToBase64(f.files[0]);
    let canvas = document.createElement('canvas');
    //canvas.getContext('2d').drawImage(Base64, 0, 0);
    let jpeg = canvas.toDataURL("image/jpeg");
  }

  // Helper converts file to base64
  function convertToBase64(file) {

    this.fileReader = new FileReader();

    if (!file) {
      throw "Error(input): file could not be found:"
    }

    return new Promise((resolve, reject) => {
      this.fileReader.readAsDataURL(file);

      this.fileReader.onerror = (error) => {
        reject("Error(input): file could not be read" + error);
      };

      this.fileReader.onloadend = () => {
        resolve(this.fileReader.result);
      };
    });
  }

</script>