<div>
  <h1>Check File Size</h1>
  <input type="file" id="file-uploader">
  
  <div id="feedback">
    
  </div  
</div>

html {
  height: 100%;
}

body {
  background: #000000;
  color: #FFFFFF;
}

div {
  display: flex;
  justify-content: center;
  flex-direction: column;
  align-items: center;
  font-family: 'Roboto Mono', monospace;
}

div#feedback {
  padding: 15px;
}

const fileUploader = document.getElementById('file-uploader');
const feedback = document.getElementById('feedback');

fileUploader.addEventListener('change', (event) => {
  const file = event.target.files[0];
  console.log('file', file);
  
  const size = file.size;
  console.log('size', size);
  let msg = '';
  
  if (size > 1024 * 1024) {
    msg = `<span style="color:red;">The allowed file size is 1MB. The file you are trying to upload is of ${returnFileSize(size)}</span>`;
  } else {
    msg = `<span style="color:green;"> A ${returnFileSize(size)} file has been uploaded successfully. </span>`;
  }
  feedback.innerHTML = msg;
});

function returnFileSize(number) {
  if(number < 1024) {
    return number + 'bytes';
  } else if(number >= 1024 && number < 1048576) {
    return (number/1024).toFixed(2) + 'KB';
  } else if(number >= 1048576) {
    return (number/1048576).toFixed(2) + 'MB';
  }
}